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Board foot
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| board foot | |
|---|---|
| Unit of | Volume |
| Symbol | FBM |
| Conversions | |
| 1 FBM in ... | ... is equal to ... |
| SI base units | ≈0.002359737 m3 |
| US Customary | 1⁄12 ft3 |
The board foot or board-foot is a unit of measurement for the volume of lumber in the United States and Canada.[1] It equals the volume of a board that is one foot (30.5 cm) in length, one foot in width, and one inch (2.54 cm) in thickness, or exactly 2.359737216 liters. Board foot can be abbreviated as FBM (for "foot, board measure"), BDFT, or BF. A thousand board feet can be abbreviated as MFBM, MBFT, or MBF. Similarly, a million board feet can be abbreviated as MMFBM, MMBFT, or MMBF.
Until the 1970s, in Australia and New Zealand, the terms super foot and superficial foot were used with the same meaning.[2][3][4]
Description
[edit]One board foot equals:
- 1 ft × 1 ft × 1 in
- 12 in × 12 in × 1 in
- 12 ft × 1 in × 1 in
- 144 in3
- 1⁄12 ft3
- ≈ 2,360 cubic centimeters
- ≈ 2.360 liters
- ≈ 0.002360 cubic meters or steres
- 1⁄1980 Petrograd Standard of board
Usage
[edit]
The board foot is used to measure both rough (unprocessed) lumber and planed (surfaced) lumber. Rough lumber is measured before drying and planing, using its full sawn dimensions. Planed lumber, such as standard softwood "two by four" boards sold at retail, is measured using nominal dimensions—typically 2 by 4 inches (50 mm × 100 mm)—even though the actual size is only about 1+1⁄2 in × 3+1⁄2 in (38 mm × 89 mm) after processing. Despite the reduction in size due to drying and planing, nominal dimensions are still used when calculating board feet for surfaced softwood lumber. This convention simplifies pricing and standardization but may result in board footage values that do not reflect the true volume of wood in the final product. Essentially, the nominal dimensions assume a larger volume than the actual board contains, which is especially relevant when estimating material needs or costs.[5] For planed lumber, board footage is calculated using the nominal width and thickness, and the actual length of the board. This reflects the lumber’s original rough size before drying and surfacing. For rough lumber, board footage is calculated using the actual width, thickness, and length of the board.
See dimensional lumber for a full explanation of nominal versus actual dimensions. Briefly, for softwoods:
- Subtract 1⁄4 inch (6 mm) from nominal sizes under 2 inches,
- Subtract 1⁄2 inch (13 mm) from nominal sizes between 2 and 8 inches,
- Subtract 3⁄4 inch (19 mm) for nominal sizes over 8 inches.[6]
The system is less complex for hardwoods, because actual board measurements are used.
Board feet can also be used a measure for the volume of logs, namely the estimated total volume of lumber that will result once a sawlog is processed on a sawmill. A variety of formulas and tables, for instance the Doyle Log Rule, exist to calculate this for a log based on its diameter and length, taking into account taper, saw kerf, and waste from cutting. [7]
See also
[edit]References
[edit]- ^ Board foot
- ^ Rowlett, Russ. "How Many? A Dictionary of Units of Measurement". Retrieved 2007-01-30.
- ^ Burger, Les. "Cutting Timber on Springbrook in 1935". Archived from the original on September 17, 2007. Retrieved 2007-11-06. Archived 2007-09-17 at the Wayback Machine
- ^ Holgate, Alan. "The Bendigo Monier Arch Bridges". Archived from the original on 2007-07-02. Retrieved 2007-11-06. Archived 2007-07-02 at the Wayback Machine
- ^ Sluga, Doug (March 21, 2025). "Board Footage Calculator for Lumber Measurements". Today’s Homeowner. Retrieved April 25, 2025.
- ^ "Softwood Lumber - Dimensions". The Engineering ToolBox. Retrieved April 25, 2025.
- ^ Bond, Brian. "Understanding Log Scales and Rules". University of Tennessee (Agricultural Extension Service). Retrieved 2 September 2025.
External links
[edit]Board foot
View on Grokipediafrom Grokipedia
Definition and Fundamentals
Definition
A board foot is a unit of volume used to measure lumber, defined as the amount of wood in a board that is nominally 12 inches long, 12 inches wide, and 1 inch thick.[9] This equates to 144 cubic inches.[1] In metric terms, one board foot is approximately 2,360 cubic centimeters.[9] The board foot is specifically designed to quantify lumber volume based on nominal dimensions—the standard labeled sizes—rather than the actual sawn dimensions, which are typically smaller after drying and planing processes.[10] This approach simplifies estimation and trade by standardizing measurements for rough lumber without requiring precise adjustments for shrinkage or surfacing.[11] As a non-SI imperial unit, the board foot is primarily employed in the United States and Canada for buying, selling, and inventorying rough lumber in the timber industry.[9][12]Relation to Volume
The board foot serves as a unit of volume specifically tailored to lumber measurement, equivalent to one-twelfth of a cubic foot. This volumetric relation stems from its definition as the space occupied by a plank measuring 1 foot in length, 1 foot in width, and 1 inch in thickness, yielding 144 cubic inches. A cubic foot, by contrast, encompasses 1,728 cubic inches (12 × 12 × 12), resulting in the precise ratio of 144 / 1,728 = 1/12 cubic foot.[13] In application to wood, the board foot quantifies gross volume, representing the overall dimensional space of the lumber piece without deductions for internal voids, such as those caused by knots, checks, or other defects. It also disregards moisture content, which influences wood weight and shrinkage but not the initial volumetric assessment. Although wood density varies significantly across species—ranging from about 20 to 60 pounds per cubic foot for common softwoods and hardwoods—the board foot remains a density-independent measure, focusing solely on geometric volume to standardize trade and estimation.[14] Practically, board foot calculations rely on nominal dimensions, which denote the approximate size of rough-sawn lumber prior to drying and planing. These processes reduce the material's thickness and width to achieve smooth surfaces and account for shrinkage, causing the actual physical volume to be less than the nominal volume—typically 10-20% lower for larger timbers, though up to 35% for smaller dimensional pieces like 2x4s. For instance, a nominal 4x4 post has an actual cross-section of about 3.5x3.5 inches after surfacing, reducing its volume by roughly 23% relative to the nominal. This discrepancy underscores the board foot's role as a conventional trade unit rather than a precise measure of final wood content.[13]Calculation Methods
Standard Formula
The standard formula for calculating board feet (BF) in lumber is given by where is the thickness in inches, is the width in inches, and is the length in feet.[15][16] This equation yields the volume of wood in board feet, a unit representing 144 cubic inches.[17] The derivation stems from defining one board foot as the volume of a rectangular prism measuring 12 inches long, 12 inches wide, and 1 inch thick, equating to 144 cubic inches; thus, the total volume in cubic inches (calculated as ) divided by 144 simplifies to the formula above when length is expressed in feet.[18][19] For non-rectangular or irregular lumber shapes, such as slabs or crooked boards, the standard approach involves approximating the volume by dividing the piece into smaller rectangular segments, calculating the board feet for each using the formula, and summing the results; alternatively, average dimensions (e.g., mean thickness and width measured at multiple points along the length) can be used as inputs to the formula, often with a scaling factor to account for voids or taper based on visual inspection or caliper measurements.[20][21] A representative example is a nominal 2x4x8 lumber piece, where inches, inches, and feet, yielding board feet.[22]Practical Examples
To illustrate the standard board foot formula in practice, consider a single board that is nominally 1 inch thick, 6 inches wide, and 10 feet long. The calculation proceeds as follows: multiply the thickness (1 inch) by the width (6 inches) by the length (10 feet), then divide by 12, yielding (1 × 6 × 10) / 12 = 5 board feet. For batch calculations involving multiple identical pieces, first determine the board feet for one item and then multiply by the quantity. For example, a nominal 2×6 board that is 12 feet long has (2 × 6 × 12) / 12 = 12 board feet; thus, a stack of 10 such boards totals 120 board feet. Lumber is typically sold based on nominal dimensions, but the actual volume after surfacing (planing) is smaller due to material removal. A nominal 2×10 board that is 16 feet long calculates to (2 × 10 × 16) / 12 ≈ 26.67 board feet using nominal sizes; however, after surfacing to actual dimensions of 1.5 inches thick by 9.25 inches wide, the volume is (1.5 × 9.25 × 16) / 12 ≈ 18.5 board feet, representing roughly a 30% reduction from the nominal value.[23] For larger construction projects, such as building a cabin, accurate estimation of required board feet involves obtaining architectural plans with a detailed bill of materials specifying lumber quantities and dimensions. Online framing calculators can then be used by inputting exact specifications, such as wall widths and stud spacing, to compute total lumber needs in board feet. It is advisable to take these plans to a lumber yard for a precise material takeoff and quote, as yard professionals can provide refined estimates based on practical experience. Additionally, factor in 10–20% extra material to account for waste from cuts, errors, and defects.[24][25][26] A common error in board foot calculations arises from failing to convert length to feet before dividing; for instance, using inches for length without adjustment (e.g., treating 10 feet as 120 inches and dividing by 144 instead of 12) leads to incorrect results, as the standard method requires length in feet.[27]Historical Development
Origins in North America
The board foot, a unit representing the volume of a board one foot long, one foot wide, and one inch thick, emerged in the early 17th century within the British North American colonies, particularly in New England, where settlers rapidly exploited vast forests to meet local construction needs and support emerging industries like shipbuilding. The first sawmills appeared around 1630, powered by water to overcome labor shortages, and by 1646, the inaugural patent for mechanical improvements to a sawmill was granted to Joseph Jenks in Lynn, Massachusetts, facilitating efficient lumber production for both domestic use and export. Shipbuilding, a key driver, began as early as 1631 with the construction of the Blessing of the Bay in Massachusetts, relying on local white pine and oak for hulls and masts, while the first mast shipment to England occurred in 1634 to supply the Royal Navy. This period marked the transition from rudimentary hand-sawing to organized timber harvesting, fueled by the colonies' abundant woodlands covering nearly all of New England. The unit's roots trace to adaptations of earlier English "board" measures, which quantified sawn lumber linearly or by stack volume, but in the colonial context, it evolved toward a foot-based volumetric standard to standardize trade amid growing exports of pine boards and clapboards to the West Indies and Europe. By the mid-17th century, production records from New England sawmills explicitly referenced board feet; for instance, colonial trade records from the Massachusetts Bay Colony further illustrate early adoption, including a 1655 General Court order appointing sworn measurers in Boston, Charlestown, and Salem to ensure accurate gauging of boards and wood for commerce, and a 1660 authorization for Boston to oversee lumber surveys within its limits. A notable example from the period involved early sawmills producing thousands of feet of boards, highlighting the unit's role in quantifying output for export-oriented operations.[28] This development was propelled by the region's dense forests—estimated to have supplied materials for an annual cut exceeding needs for local building—and escalating demands from European markets for ship timber and building materials, all occurring well before American independence in 1776. Timber exports supported the colonial economy from the 1640s onward, with pine boards from Massachusetts Bay becoming a staple in transatlantic trade, underscoring the board foot's practical origins in resource-rich, export-driven colonial enterprise.Standardization Efforts
In the 19th century, the expansion of interstate and international lumber trade in North America highlighted inconsistencies in board foot calculations, often stemming from varying log scaling rules such as the Doyle rule (developed around 1825) and the Scribner rule (introduced in the 1840s), which led to frequent disputes over volume estimates and pricing.[29][30] To mitigate these issues, lumber associations, including the American Forestry Association founded in 1875, advocated for more uniform measurement practices, laying the groundwork for later formal standards.[31] These early efforts focused on resolving regional variations in how board feet were derived from rough lumber dimensions, emphasizing the need for a consistent unit to facilitate fair commerce across distant markets.[32] The 20th century saw the codification of these initiatives through institutional involvement, beginning with the establishment of the U.S. Forest Products Laboratory (FPL) in 1910 by the USDA Forest Service, which conducted empirical research to validate board foot measurements against actual lumber yields from logs.[33] The FPL's testing programs helped standardize the unit by quantifying shrinkage and recovery factors, confirming its reliability as a national benchmark for softwood and hardwood volumes. In the 1920s, the U.S. National Bureau of Standards (predecessor to NIST) incorporated the board foot into official guidelines via Simplified Practice Recommendation No. 16 (1924), which defined nominal sizes and volume calculations for dimension lumber and boards to promote uniformity in production and trade.[34] Further refinement occurred in the 1940s with ASTM International's adoption of standard D245, initially issued as a tentative method in 1926 and revised in the early 1940s, which established procedures for adjusting structural properties of visually graded lumber based on board foot volumes and size factors.[35] This standard addressed grading for ties and other products, ensuring the board foot's integration into engineering specifications. Despite pushes for metric conversion in the 1970s, the board foot endured in North American lumber practices due to its widespread adoption and the industry's resistance to overhauling entrenched systems.[36]Comparisons with Other Units
Metric Equivalents
The board foot, defined as the volume of a board 1 foot long, 1 foot wide, and 1 inch thick, equates exactly to 144 cubic inches. Converting this to metric units yields a precise volume of 2,359.737 cubic centimeters (cm³) or approximately 0.002359737 cubic meters (m³), based on the international standard where 1 inch equals 25.4 millimeters exactly. In practical applications, the board foot is often approximated as equivalent to 2.36 liters of volume, facilitating quick mental conversions in lumber handling.[37] The following table provides common equivalents for multiples of board feet (BF) to cubic meters (m³), using the approximation of 0.00236 m³ per BF as per UNECE guidelines, rounded to three decimal places for usability:| Board Feet (BF) | Cubic Meters (m³) |
|---|---|
| 1 | 0.002 |
| 10 | 0.024 |
| 100 | 0.236 |
| 1,000 | 2.360 |
| 10,000 | 23.600 |
m³ = BF × 0.002359737.
For example, in a lumber shipment of 500 board feet:
- Multiply 500 by 0.002359737 = 1.1798685.
- Round to appropriate precision, such as 1.180 m³, for billing or inventory purposes. This method ensures accurate volume assessment in metric-dominant regions.