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Fahrenheit
Thermometer with Fahrenheit (marked on outer bezel) and Celsius (marked on inner dial) degree units.
General information
Unit systemImperial/US customary
Unit ofTemperature
Symbol°F
Named afterDaniel Gabriel Fahrenheit
Conversions
x °F in ...... corresponds to ...
   Kelvin scale   ⁠5/9⁠(x + 459.67) K
   Celsius scale   ⁠5/9⁠(x − 32) °C
   Rankine scale   x + 459.67 °Ra

The Fahrenheit scale (/ˈfærənhaɪt, ˈfɑːr-/) is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736).[1] It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined his scale exist, but the original paper suggests the lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from a mixture of water, ice, and ammonium chloride (a salt).[2][3] The other limit established was his best estimate of the average human body temperature, originally set at 90 °F, then 96 °F (about 2.6 °F less than the modern value due to a later redefinition of the scale).[2]

For much of the 20th century, the Fahrenheit scale was defined by two fixed points with a 180 °F separation: the temperature at which pure water freezes was defined as 32 °F and the boiling point of water was defined to be 212 °F, both at sea level and under standard atmospheric pressure. It is now formally defined using the Kelvin scale.[4][5]

It continues to be used in the United States (including its unincorporated territories), its freely associated states in the Western Pacific (Palau, the Federated States of Micronesia and the Marshall Islands), the Cayman Islands, and Liberia.

Fahrenheit is commonly still used alongside the Celsius scale in other countries that use the U.S. metrological service, such as Antigua and Barbuda, Saint Kitts and Nevis, the Bahamas, and Belize. A handful of British Overseas Territories, including the Virgin Islands, Montserrat, Anguilla, and Bermuda, also still use both scales.[6] All other countries now use Celsius ("centigrade" until 1948), which was developed over 18 years after the Fahrenheit scale.[7]

Definition and conversion

[edit]
Fahrenheit temperature conversion formulae
from Fahrenheit to Fahrenheit
Celsius x °F ≘ (x − 32) × ⁠5/9⁠ °C x °C ≘ (x × ⁠9/5⁠ + 32) °F
Kelvin x °F ≘ (x + 459.67) × ⁠5/9⁠ K x K ≘ (x × ⁠9/5⁠ − 459.67) °F
Rankine x °F ≘ (x + 459.67) °R x °R ≘ (x − 459.67) °F
For temperature intervals rather than specific temperatures,
1 °F = 1 °R = ⁠5/9⁠ °C = ⁠5/9⁠ K
Conversion between temperature scales

Historically, on the Fahrenheit scale the freezing point of water was 32 °F, and the boiling point was 212 °F (at standard atmospheric pressure). This put the boiling and freezing points of water 180 degrees apart.[8] Therefore, a degree on the Fahrenheit scale was 1⁄180 of the interval between the freezing point and the boiling point. On the Celsius scale, the freezing and boiling points of water were originally defined to be 100 degrees apart. A temperature interval of 1 °F was equal to an interval of 5⁄9 degrees Celsius. With the Fahrenheit and Celsius scales now both defined by the kelvin, this relationship was preserved, a temperature interval of 1 °F being equal to an interval of 5⁄9 K and of 5⁄9 °C. The Fahrenheit and Celsius scales intersect numerically at −40 in the respective unit (i.e., −40 °F corresponds to −40 °C).

Absolute zero is 0 K, −273.15 °C, or −459.67 °F. The Rankine temperature scale uses degree intervals of the same size as those of the Fahrenheit scale, except that absolute zero is 0 °R – the same way that the Kelvin temperature scale matches the Celsius scale, except that absolute zero is 0 K.[8]

The combination of degree symbol (°) followed by an uppercase letter F is the conventional symbol for the Fahrenheit temperature scale. A number followed by this symbol (and separated from it with a space) denotes a specific temperature point (e.g., "Gallium melts at 85.5763 °F"). A difference between temperatures or an uncertainty in temperature is also conventionally written the same way as well, e.g., "The output of the heat exchanger experiences an increase of 72 °F" or "Our standard uncertainty is ±5 °F". However, some authors instead use the notation "An increase of 50 F°" (reversing the symbol order) to indicate temperature differences. Similar conventions exist for the Celsius scale, see Celsius § Temperatures and intervals.[9][10]

Conversion (specific temperature point)

[edit]

For an exact conversion between degrees Fahrenheit and Celsius, and kelvins of a specific temperature point, the following formulas can be applied. Here, f is the value in degrees Fahrenheit, c the value in degrees Celsius, and k the value in kelvins:

  • f °F to c °C: c = ⁠f − 32/1.8⁠
  • c °C to f °F: f = c × 1.8 + 32
  • f °F to k K: k = ⁠f + 459.67/1.8⁠
  • k K to f °F: f = k × 1.8 − 459.67

There is also an exact conversion between Celsius and Fahrenheit scales making use of the correspondence −40 °F ≘ −40 °C. Again, f is the numeric value in degrees Fahrenheit, and c the numeric value in degrees Celsius:

  • f °F to c °C: c = ⁠f + 40/1.8⁠ − 40
  • c °C to f °F: f = (c + 40) × 1.8 − 40

Conversion (temperature difference or interval)

[edit]

When converting a temperature interval between the Fahrenheit and Celsius scales, only the ratio is used, without any constant (in this case, the interval has the same numeric value in kelvins as in degrees Celsius):

  • f °F to c °C or k K: c = k = ⁠f/1.8⁠
  • c °C or k K to f °F: f = c × 1.8 = k × 1.8

History

[edit]

Fahrenheit proposed his temperature scale in 1724, basing it on two reference points of temperature. In his initial scale (which is not the final Fahrenheit scale), the zero point was determined by placing the thermometer in "a mixture of ice, water, and salis Armoniaci[note 1] [transl. ammonium chloride] or even sea salt".[11] This combination forms a eutectic system, which stabilizes its temperature automatically: 0 °F was defined to be that stable temperature. A second point, 96 degrees, was approximately the human body's temperature.[11] A third point, 32 degrees, was marked as being the temperature of ice and water "without the aforementioned salts".[11]

According to a German story, Fahrenheit actually chose the lowest air temperature measured in his hometown Danzig (Gdańsk, Poland) in winter 1708–09 as 0 °F, and only later had the need to be able to make this value reproducible using brine.[12][failed verification]

According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[13] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by 4 in order to eliminate fractions and make the scale more fine-grained. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees, and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval 6 times (since 64 = 26).[14][15]

Fahrenheit soon after observed that water boils at about 212 degrees using this scale.[16] The use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of Anders Celsius, and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776–77.[17][18] Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water was exactly 32 °F, and the boiling point was exactly 212 °F, or 180 degrees higher. It is for this reason that normal human body temperature is approximately 98.6 °F (oral temperature) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale).[19]

In the present-day Fahrenheit scale, 0 °F no longer corresponds to the eutectic temperature of ammonium chloride brine as described above. Instead, that eutectic is at approximately 4 °F on the final Fahrenheit scale.[note 2]

The Rankine temperature scale was based upon the Fahrenheit temperature scale, with its zero representing absolute zero instead.

Usage

[edit]

General

[edit]
Countries by usage:
  Fahrenheit (°F)
  Fahrenheit (°F) and Celsius (°C)
  Celsius (°C)

The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in Anglophone countries until the 1960s. In the late 1960s and 1970s, the Celsius scale replaced Fahrenheit in almost all of those countries—with the notable exception of the United States.

Fahrenheit is used in the United States, its territories and associated states (all serviced by the U.S. National Weather Service), as well as the (British) Cayman Islands and Liberia for everyday applications. The Fahrenheit scale is in use in U.S. for all temperature measurements including weather forecasts, cooking, and food freezing temperatures; however, for scientific research, the scale is Celsius and Kelvin.[20]

United States

[edit]

Early in the 20th century, Halsey and Dale suggested that reasons for resistance to the use of the centigrade (now Celsius) system in the U.S. included the larger size of each degree Celsius and the lower zero point in the Fahrenheit system; and claimed the Fahrenheit scale is more intuitive than Celsius for describing outdoor temperatures in temperate latitudes, with 100 °F being a hot summer day and 0 °F a cold winter day.[21]

Canada

[edit]

Canada has passed legislation favoring the International System of Units, while also maintaining legal definitions for traditional Canadian imperial units.[22] Canadian weather reports are conveyed using degrees Celsius with occasional reference to Fahrenheit especially for cross-border broadcasts. Fahrenheit is still used on virtually all Canadian ovens.[23] Thermometers, both digital and analog, sold in Canada usually employ both the Celsius and Fahrenheit scales.[24][25][26]

European Union

[edit]

In the European Union, it is mandatory to use Kelvins or degrees Celsius when quoting temperature for "economic, public health, public safety and administrative" purposes, though degrees Fahrenheit may be used alongside degrees Celsius as a supplementary unit.[27]

United Kingdom

[edit]

Most British people use Celsius.[28] However, the use of Fahrenheit still may appear at times alongside degrees Celsius in the print media with no standard convention for when the measurement is included.

For example, The Times has an all-metric daily weather page but includes a Celsius-to-Fahrenheit conversion table.[29] Some UK tabloids have adopted a tendency of using Fahrenheit for mid to high temperatures.[30] It has been suggested that the rationale to keep using Fahrenheit was one of emphasis for high temperatures: "−6 °C" sounds colder than "21 °F", and "94 °F" sounds more sensational than "34 °C".[31]

Unicode representation of symbol

[edit]

Unicode provides the Fahrenheit symbol at code point U+2109 ℉ DEGREE FAHRENHEIT. However, this is a compatibility character encoded for roundtrip compatibility with legacy encodings. The Unicode standard explicitly discourages the use of this character: "The sequence U+00B0 ° DEGREE SIGN + U+0046 F LATIN CAPITAL LETTER F is preferred over U+2109 ℉ DEGREE FAHRENHEIT, and those two sequences should be treated as identical for searching."[32]

See also

[edit]

Notes

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Fahrenheit

View on Grokipedia
from Grokipedia
The Fahrenheit scale is a system proposed by German-Dutch physicist and instrument maker in 1724, defining the freezing point of water as 32° and its as 212° at standard atmospheric pressure./03:_Measurements/3.10:_Temperature_and_Temperature_Scales) Fahrenheit calibrated the scale using empirical reference points, including 0° for the chilling mixture of ice, water, and —a reproducible low —and initially approximating at 96°, later refined to about 98.6°. This results in 180 divisions between freezing and boiling, providing smaller degree increments for distinguishing subtle temperature differences in ambient conditions compared to the scale's 100-degree span./03:_Measurements/3.10:_Temperature_and_Temperature_Scales) Despite international standardization on via the , Fahrenheit persists officially in the United States, , , and several smaller nations and territories, reflecting historical imperial measurement traditions and practical inertia in sectors like , cooking, and HVAC. Fahrenheit's concurrent invention of the mercury thermometer enabled the scale's precision, marking a key advance in accurate thermometry over prior alcohol-based devices.

Definition and Scale

Defining Temperatures and Intervals

The Fahrenheit scale (°F) is defined by assigning the freezing point of at standard (1 atm or 101.325 kPa) to 32 °F and the normal of to 212 °F, creating a span of 180 °F between these empirical fixed points used for ./12:_Temperature_and_Kinetic_Theory/12.2:_Temperature_and_Temperature_Scales) These points provide reference temperatures for thermometers, with the ice- equilibrium serving as the lower anchor and the steam- equilibrium at sea-level as the upper./12:_Temperature_and_Kinetic_Theory/12.2:_Temperature_and_Temperature_Scales) A single degree Fahrenheit represents 1/180th of the interval between the freezing and points of , making the Fahrenheit degree smaller than the degree by a factor of 5/9. This interval size ensures that temperature differences, such as a change of 1 °F, correspond to equivalent thermal expansions in materials like mercury or alcohol in thermometers calibrated to the scale./12:_Temperature_and_Kinetic_Theory/12.2:_Temperature_and_Temperature_Scales) In thermodynamic terms, the scale aligns with the International Temperature Scale (ITS-90) through conversion from , where the of is precisely 32.018 °F, though practical definitions retain the nominal 32 °F and 212 °F for most applications. For absolute temperature measurements, the (°R) uses the same degree interval as Fahrenheit but sets at 0 °R, equivalent to -459.67 °F, preserving the granularity of Fahrenheit intervals in engineering contexts like . This equivalence underscores that Fahrenheit intervals measure proportional changes in , with 1 °F = 1 °R = 5/9 in magnitude, independent of the arbitrary zero point.

Conversion Formulas

The Fahrenheit (°F) and (°C) temperature scales differ in both their zero points and degree sizes, necessitating specific conversion formulas. The freezing point of is 32°F (0°C), and the boiling point is 212°F (100°C), establishing an offset of 32 degrees and a scale factor where one Fahrenheit degree equals 5/9 of a degree. To convert from to Fahrenheit, the formula is F=(C×95)+32F = (C \times \frac{9}{5}) + 32. Conversely, to convert from Fahrenheit to , C=(F−32)×59C = (F - 32) \times \frac{5}{9}. These equations account for both the additive shift and the proportional scaling between the intervals. For relation to the scale, which is the SI absolute temperature scale with 0 at , first convert Fahrenheit to and then add 273.15: K=[(F−32)×59]+273.15K = [(F - 32) \times \frac{5}{9}] + 273.15. This yields exact conversions, as the - relation is K=C+273.15K = C + 273.15, preserving the Fahrenheit adjustments.

Historical Development

Origins and Invention

was born on May 24, 1686, in Danzig (present-day , ), into a prosperous family of German descent. Orphaned by age 15 following a family outbreak of mushrooms, he was apprenticed to a but developed a keen interest in scientific instruments during travels across , particularly in chemistry and physics. Settling in by the early 1700s as a maker of scientific instruments, Fahrenheit focused on improving thermometers, which suffered from inconsistencies in materials and amid the proliferation of over 35 competing scales by that era. In 1708, Fahrenheit encountered Danish astronomer in , adopting Rømer's techniques for sealing thermometers to prevent fluid expansion and contraction errors, as well as Rømer's early scale with finer graduations. Building on this, Fahrenheit introduced the mercury thermometer in 1714, leveraging mercury's higher , uniform expansion, and visibility for superior precision over alcohol or wine-spirit variants, enabling reliable measurements across wider ranges. Fahrenheit formalized his eponymous scale in a 1724 paper submitted to the Royal Society's Philosophical Transactions, defining it via three fixed points for reproducibility: 0° as the temperature of a mixture (, , and or common salt), representing a practical artificial cold around -18°C; 32° as the freezing/ of pure at standard pressure; and 96° as average under the armpit. The choice of 32° and 96° yielded a 64° interval—2⁶—highly divisible by 2, 4, 8, 16, and 32, permitting subdivisions into halves, quarters, and eighths without fractions, which suited the era's instrument-making precision before decimal systems dominated. This adjustment stemmed from an earlier calibration where froze at 30° and body temperature at 90°, but Fahrenheit refined it for better divisibility while retaining the brine zero. 's boiling point registered at 212° under the scale, later confirmed empirically.

Early Adoption and Standardization

Fahrenheit's and associated scale, first described in a paper to the Royal Society, gained initial traction among instrument makers and scientists in the , where he resided and produced devices commercially. His instruments, prized for their precision and reproducibility using mercury over alcohol, were exported across , with early users including Dutch and German scholars experimenting in physics and . By the , Fahrenheit thermometers appeared in English scientific circles, facilitated by his election to the Royal Society in , which elevated his reputation and promoted the scale's fixed points—zero at a brine-ice mixture and 96° for approximate —for consistent calibration. Adoption accelerated in Britain during the mid-18th century, as the scale's finer graduations (smaller degree intervals than contemporaries like Réaumur) suited meteorological and clinical observations, outperforming earlier inconsistent alcohol thermometers. British instrument makers, such as those in , replicated Fahrenheit's designs, embedding the scale in weather records and naval logs by the . In the American colonies, reliant on British imports and scientific exchanges, Fahrenheit thermometers entered use for agriculture, shipping, and early activities, with figures like referencing Fahrenheit readings in 18th-century correspondence. Formal standardization emerged in the 1770s, when British scientists, amid debates over competing scales like Linnaeus's centigrade proposal (later refined as Celsius in 1742), endorsed Fahrenheit for imperial consistency, extending it across the Empire's observatories and standards bodies. This imperial decree solidified its role in English-speaking domains, predating Celsius standardization elsewhere by years and resisting continental metric shifts. Post-1776, the newly independent United States inherited and codified Fahrenheit in customary practices, with no legislative override until 20th-century metrication attempts, preserving it as the de facto standard for public and industrial measurement.

Technical Properties

Relation to Physical Phenomena

The Fahrenheit scale's reference points are grounded in empirical physical phenomena, specifically phase transitions and reproducible thermal equilibria. In its original formulation by around , the zero point (0 °F) was defined as the freezing temperature of a solution composed of , water, and (NH₄Cl), achieving a eutectic mixture that freezes uniformly at approximately −17.8 °C due to the specific composition where solid salts, , and saturated solution coexist in equilibrium. This provided a stable, low-temperature anchor independent of varying ambient conditions, leveraging the of eutectic freezing for consistent in early thermometry. Subsequent calibration incorporated the melting/freezing point of pure at 32 °F, marking the (0 °C at standard ) where liquid and are in dynamic equilibrium, absorbing or releasing of fusion (334 J/g) without change until the completes. The was established at 212 °F, corresponding to the vaporization equilibrium of at 1 (100 °C), where of (2260 J/g) facilitates the liquid-to-gas transition, with the exact value sensitive to variations as described by the Clausius-Clapeyron relation. These water-based fixed points tie the scale to H₂O's intrinsic thermodynamic properties, including maxima at 4 °C and thermal expansion coefficients, though offset by 32 °F from zero for historical reproducibility. An additional reference was human body temperature, initially set near 96–100 °F to reflect axillary or oral thermal equilibrium (around 37 °C), a physiological steady-state maintained by metabolic heat production balancing conductive, convective, and radiative losses. This biological-physical benchmark, later refined to 98.6 °F via more precise measurements, underscores the scale's empirical origins in observable thermal states rather than absolute thermodynamic zero. Unlike the Kelvin scale's extrapolation from gas laws to absolute zero (−273.15 °C or 0 K), Fahrenheit prioritizes accessible phase-change anchors, yielding a degree interval of 1/180th between water's freezing and boiling—finer than Celsius's 1/100th for resolving small physical variations in ambient or material responses.

Comparison with Celsius and Kelvin Scales

The Fahrenheit scale defines the freezing point of water at 32 °F and the boiling point at 212 °F at standard atmospheric pressure, spanning 180 degrees between these points. In comparison, the Celsius scale sets these reference points at 0 °C and 100 °C, respectively, covering 100 degrees, while the Kelvin scale, the SI unit of thermodynamic temperature, locates them at 273.15 K and 373.15 K. The Kelvin scale is absolute, with 0 K defined as absolute zero, equivalent to -273.15 °C or -459.67 °F, prohibiting negative temperatures and aligning directly with the Boltzmann constant for thermodynamic relations. Celsius and Kelvin share identical interval sizes, where one degree Celsius equals one kelvin, differing only by an offset of 273.15 K; thus, the conversion is K=°C+273.15K = °C + 273.15. The Fahrenheit degree is smaller, with one Celsius degree or kelvin corresponding to 1.8 Fahrenheit degrees, reflecting the 180-degree span versus 100 in Celsius/Kelvin between water's phase change points. Conversion between Fahrenheit and Celsius uses the formula °C=(°F−32)×59°C = (°F - 32) \times \frac{5}{9}, or inversely °F=°C×95+32°F = °C \times \frac{9}{5} + 32; for Kelvin, intermediate conversion through Celsius is standard.
Reference PointFahrenheit (°F)Celsius (°C)Kelvin (K)
Absolute zero-459.67-273.150
Freezing point of water320273.15
Boiling point of water212100373.15
These differences arise from historical calibrations: Fahrenheit's scale draws from empirical points like a mixture (0 °F) and approximations, whereas prioritizes water's phase transitions for metric alignment, and ensures proportionality to for scientific applications. In practice, Fahrenheit provides finer granularity (smaller degree size) for temperatures in the human-comfortable range around 0 to 100 °F, equivalent to roughly -18 to 38 °C, but lacks the absolute reference of , which is mandatory in international scientific contexts.

Merits and Debates

Practical Advantages for Everyday and Human-Centric Measurement

The Fahrenheit scale provides finer granularity for temperature measurements relevant to experience, as each degree Fahrenheit corresponds to approximately 5/9 of a degree, enabling distinctions of smaller increments without decimal places in applications such as settings and forecasts. This precision aligns with human sensory capabilities, where differences of 1°F in air are perceptible, facilitating more accurate adjustments in (HVAC) systems for occupant comfort. In physiological contexts, the scale centers normal human core body temperature at 98.6°F, allowing straightforward assessment of deviations like mild fevers at 100–102°F or risks below 95°F, which correspond to narrower margins in and reduce for medical monitoring and communication. Everyday ambient comfort zones, such as room temperatures around 68–77°F for sedentary activities, span a 9-degree range that captures perceptible shifts in sensation, supporting intuitive decisions in clothing, activity levels, and indoor climate control without frequent reference to conversion formulas. For practical domains like cooking and baking, the smaller degree size permits precise recipe instructions—e.g., increments of 25°F for oven adjustments—enhancing reproducibility and safety in home and professional settings where subtle variations affect outcomes, such as or doneness. Similarly, in for non-scientific audiences, Fahrenheit's typical daily ranges in temperate regions (e.g., 32–86°F) avoid routine negatives and align with a 0–100 span that intuitively evokes tolerance limits, aiding quick comprehension of risk or heat stress without mental arithmetic.

Criticisms and Rebuttals Regarding Scientific Utility

Critics of the Fahrenheit scale argue that its reference points lack direct correspondence to fundamental physical phenomena, rendering it less suitable for scientific applications compared to the or scales. The zero point was originally set at the freezing temperature of a solution (a of water, ice, and ), while 96 degrees approximated normal , later adjusted to align water's freezing at 32 degrees and at 212 degrees under standard conditions. This arbitrary foundation contrasts with , which defines 0 degrees as pure water's freezing point and 100 degrees as its at sea-level , facilitating reproducible experiments tied to phase transitions. Further criticisms highlight the scale's incompatibility with the (SI), where serves as the base temperature unit, defined via the and (0 K = -273.15°C), enabling precise thermodynamic calculations without negative values or arbitrary offsets. Fahrenheit's non-metric intervals—spanning 180 degrees between water's freezing and points versus 's 100—introduce awkward conversion factors (e.g., °F = °C × 9/5 + 32), complicating international collaboration and data integration in fields like physics, chemistry, and . from scientific publishing supports this: peer-reviewed journals overwhelmingly report temperatures in or , with Fahrenheit appearing primarily in U.S.-centric contexts rather than pure , as adoption of SI standards post-1960s prioritized uniformity. Proponents rebut that Fahrenheit's finer degree increments (1°F ≈ 0.556°C) provide greater granularity for measuring subtle variations in ambient or human-relevant temperatures, potentially reducing reliance on decimal places in or data logging. For instance, distinguishing between 70°F and 71°F equates to a 0.556°C change, versus 21°C to 21.556°C in , which some argue enhances precision in non-absolute contexts like without invoking Kelvin's full scale. However, this advantage is contested on grounds that scientific precision derives from instrumental resolution and statistical methods, not scale choice; users routinely employ decimals or millidegrees, and Kelvin's absolute framework better supports equations involving or entropy, where Fahrenheit's offset (e.g., negative values above ) adds computational friction. In practice, the debate underscores convention over inherent flaws: while Fahrenheit's historical precision suited early thermometry, global favors / for , as evidenced by the near-universal shift to metric systems in post-World War II, minimizing errors in cross-border datasets. Rebuttals emphasizing Fahrenheit's utility often pertain to everyday or industrial applications rather than theoretical science, where causal relations to physical constants prioritize SI alignment.

Global Usage Patterns

Primary Users: United States and Territories

The employs the Fahrenheit scale as the standard for temperature measurement in public weather forecasts, everyday applications such as cooking and heating/ventilation/air conditioning (HVAC) systems, and consumer products like thermometers. The (NWS), under the (NOAA), issues forecasts and observations primarily in degrees Fahrenheit for surface-level weather across the country, reflecting its persistence in official meteorological reporting despite the 1975 designating the as the preferred system of weights and measures. This usage aligns with broader adoption of U.S. customary units in non-scientific contexts, where Fahrenheit provides finer granularity for human-perceived temperature ranges, such as distinguishing between 70°F and 75°F in comfortable indoor settings. U.S. territories, including , , the , , and the , follow the same convention, with weather services integrated into the NWS framework delivering Fahrenheit-based reports. In , for instance, daily weather announcements and public advisories use Fahrenheit, though Celsius appears alongside it in some educational or scientific contexts due to bilingual influences and occasional metric education efforts. These territories, as unincorporated U.S. possessions, inherit federal standards for measurement, ensuring consistency in , maritime, and emergency communications where Fahrenheit dominates. Limited metrication attempts, such as in 's 1979 law recognizing both systems, have not displaced Fahrenheit in practical, public-facing uses like signage or local media. Scientific and industrial sectors in the U.S. and territories increasingly adopt or for precision and international compatibility, as mandated in fields like and , but Fahrenheit remains entrenched in consumer and regulatory domains. For example, FDA guidelines for reference Fahrenheit thresholds, and automotive thermostats default to it. This dual-system reality underscores Fahrenheit's role as the for non-specialized users, with surveys indicating over 90% familiarity among Americans for interpreting Fahrenheit in daily scenarios. Efforts to fully transition, such as NOAA's optional inclusions in some forecasts since the , have seen negligible uptake, preserving Fahrenheit's primacy.

Limited or Transitional Use in Other Regions

Several small sovereign states outside the and its territories maintain the Fahrenheit scale as their official or primary temperature measurement system, primarily due to historical colonial legacies and economic ties to the . These nations include in , the and in the , as well as and the in the Pacific. In , for instance, reports and public thermometers routinely display temperatures in Fahrenheit, reflecting its continued everyday utility despite global metric trends. The , a British Overseas Territory, also predominantly employs Fahrenheit, influenced by tourism from the and retained imperial measurement practices, though appears alongside in some official contexts. This limited adoption underscores Fahrenheit's persistence in regions with small populations—collectively under 1 million residents—where switching costs are low but alignment provides practical benefits for and . Transitional usage occurs in countries like the , where has been statutory since 1965, yet Fahrenheit lingers informally among older demographics or in legacy references, such as historical or casual , gradually fading with generational shifts. Similarly, in , post-1975 has entrenched in public and scientific spheres, but Fahrenheit occasionally surfaces in -influenced industries like or among communities, marking a vestigial rather than operational role. These patterns highlight Fahrenheit's marginalization beyond core users, driven by international pressures without full displacement in niche locales.

Scientific and International Standards

The (SI), established by the General Conference on Weights and Measures, defines the (K) as the base unit for , with its magnitude fixed by setting the at exactly 1.380649 × 10⁻²³ J/K. This ensures measurements reflect molecular without negative values, essential for fields like and chemistry. The scale (°C), where intervals equal those of kelvin and 0 °C equals 273.15 K (the of minus 0.01 K), serves as a practical for most scientific reporting, aligning with empirical reference points like water's freezing and boiling under standard pressure. Fahrenheit (°F) holds no status within SI or international scientific standards, lacking recognition by bodies such as the International Bureau of Weights and Measures (BIPM) or the National Institute of Standards and Technology (NIST) for fundamental measurements. Conversion formulas exist for interoperability—°F = (°C × 9/5) + 32—but scientific literature and protocols universally prioritize or to maintain precision and universality, as Fahrenheit's arbitrary bracketing (water freezes at 32 °F, boils at 212 °F) introduces fractions in thermodynamic equations and complicates cross-border data sharing. For instance, ISO standards for , such as on reference temperatures, reference SI units exclusively, underscoring Fahrenheit's exclusion from global technical specifications. In practice, international organizations like the (WMO) mandate Celsius for climate data and forecasts in official exchanges, while Fahrenheit appears only in U.S.-centric contexts, such as domestic weather reports or tied to imperial systems. This divergence reflects SI's emphasis on coherence and , where Fahrenheit's finer gradations (1 °F ≈ 0.556 °C) offer no empirical advantage in absolute scaling but add conversion overhead in collaborative . Standards bodies provide Fahrenheit equivalents solely for legacy compatibility, not endorsement, ensuring SI dominance in peer-reviewed publications and .

References

  1. https://chemed.chem.purdue.edu/genchem/history/fahrenheit.html
  2. https://www.aps.org/apsnews/2022/05/fahrenheit-birth-precision-thermometry
  3. https://tutco.com/conductive/ask-ian-temperature-scales
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  24. https://chem.libretexts.org/Under_Construction/Purgatory/Introductory_Chemistry_at_Solano_College/03%253A_Unit_Systems_and_Dimensional_Analysis/3.10%253A_Temperature_and_Temperature_Scales
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  31. https://www.climateforesight.eu/interview/yes-you-can-feel-one-degree/
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  38. https://www.utdailybeacon.com/opinion/ask-a-scientist-why-was-the-fahrenheit-system-devised-the-way-it-has-been-in/article_aef03bca-7858-11e7-a513-b774dcfc4bee.html
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  42. https://usma.org/metric-system-temperature
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  44. https://www.quora.com/What-measurement-of-temperature-does-Puerto-Rico-use
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  47. https://www.worldatlas.com/articles/countries-that-use-fahrenheit.html
  48. https://www.reddit.com/r/todayilearned/comments/9dwa73/til_there_are_only_5_countries_the_bahamas_belize/
  49. https://www.quora.com/Which-countries-use-Fahrenheit-as-a-measurement-of-temperature
  50. https://www.livescience.com/temperature.html
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