Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of deaths per 1,000 individuals per year; thus, a mortality rate of 9.5 (out of 1,000) in a population of 1,000 would mean 9.5 deaths per year in that entire population, or 0.95% out of the total. It is distinct from "morbidity", which is either the prevalence or incidence of a disease, and also from the incidence rate (the number of newly appearing cases of the disease per unit of time).^{[verification needed]}

An important specific mortality rate measure is the crude death rate, which looks at mortality from all causes in a given time interval for a given population. As of 2020^[update], for instance, the CIA estimates that the crude death rate globally will be 7.7 deaths per 1,000 people in a population per year. As of 2024, the global crude death rate stood at 7.76, marking a 2.35% rise compared to 2023. In a generic form, mortality rates can be seen as calculated using ${\displaystyle (d/p)\cdot 10^{n}}$, where d represents the deaths from whatever cause of interest is specified that occur within a given time period, p represents the size of the population in which the deaths occur (however this population is defined or limited), and ${\displaystyle 10^{n}}$ is the conversion factor from the resulting fraction to another unit (e.g., multiplying by ${\displaystyle 10^{3}}$ to get mortality rate per 1,000 individuals).

The crude death rate is defined as "the mortality rate from all causes of death for a population," calculated as the "total number of deaths during a given time interval" divided by the "mid-interval population", per 1,000 or 100,000; for instance, the population of the United States was around 290,810,000 in 2003, and in that year, approximately 2,419,900 deaths occurred in total, giving a crude death (mortality) rate of 832 deaths per 100,000. As of 2020^[update], the CIA estimates the U.S. crude death rate will be 8.3 per 1,000, while it estimates that the global rate will be 7.7 per 1,000.

According to the World Health Organization, the ten leading causes of death, globally, in 2016, for both sexes and all ages, were as presented in the table below.

Crude death rate, per 100,000 population

Mortality rate is also measured per thousand. It is determined by how many people of a certain age die per thousand people. Decrease of mortality rate is one of the reasons for increase of population. Development of medical science and other technologies has resulted in the decrease of mortality rate in all the countries of the world for some decades. In 1990, the mortality rate of children under five years of age was 144 per thousand, but in 2015 the child mortality rate was 38 per thousand.^{[citation needed]}

Other specific measures of mortality include:

For any of these, a "sex-specific mortality rate" refers to "a mortality rate among either males or females", where the calculation involves both "numerator and denominator... limited to the one sex".