BMR Calculator

Basal metabolic rate, or BMR, is the lowest rate of energy expenditure that keeps you alive. It's measured while you lie down, at rest, fasting, still, at a comfortable temperature, and mentally relaxed ⁵.

BMR makes up roughly 45 to 70 percent of total energy expenditure in adults. Your gender, body size, body composition, and age mainly determine it ².

Measuring BMR directly takes a laboratory. Accurate measurement needs indirect or direct calorimetry. You must lie awake on your back, 10 to 12 hours after a meal. You need eight hours of physical rest first, with no strenuous exercise the day before. You must stay mentally relaxed, in a room that will not make you shiver or sweat ².

That setup only works for small groups studied under lab conditions. This page instead estimates BMR using predictive equations. These equations are built on past measurements like these ².

Mifflin-St Jeor is the usual first choice. The Harris-Benedict equations were derived in 1919. Those older equations overestimated measured resting energy expenditure by 5 percent ¹. This calculator uses a simplified, sex-specific version. It is 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age in years, plus 5 for men or minus 161 for women ¹.

Schofield is the equation the FAO/WHO/UNU report relied on. About half of the underlying data came from studies of Italian men in the late 1930s and 1940s. Their BMR values were relatively high, which raised questions about how well the equations apply to other groups. Even so, the report kept these equations while it waited for broader data ².

Henry, also called the Oxford equations, came later. It was built from a larger, more varied data set of 10552 BMR measurements. This set dropped the Italian subjects and added far more people from tropical regions ⁷. The UK's Scientific Advisory Committee on Nutrition adopted the weight-and-height version of Henry's equations to estimate BMR ³.

You get TDEE by multiplying BMR by an activity factor called PAL. PAL stands for physical activity level. It expresses energy need as a multiple of 24-hour BMR. You can also estimate PAL as total energy expenditure divided by BMR ².

The FAO/WHO/UNU report gives an example. It uses women aged 20 to 30 who average 55 kg and live a moderately active lifestyle. Their BMR is 5.45 MJ/day (1302 kcal/day). Multiply that by a PAL of 1.85. The result is an energy requirement of 10.08 MJ/day (2410 kcal/day) ⁴.

Mifflin-St Jeor was derived from data on 498 healthy adults aged 19 to 78 ¹. Pick that equation outside that span, and the calculator still returns a number, but flags it as outside the studied age range.

Schofield and Henry take a different approach: both publish separate equations for ages 18 to 30, 30 to 60, and over 60 ². Because every adult age has a matching band, this page always treats those two equations as covering your age.

Studies show that Schofield prediction equations may overestimate BMR in many communities. Alternative prediction equations, called the Henry equations, have also been developed ³.

Researchers tested both against a US group of people. The Henry equations predicted resting metabolic rate within plus or minus 10 percent for 79 percent of subjects. Schofield did this for only 69 percent of subjects. Both versions of Henry performed slightly better than Schofield overall ³.

The Oxford equations, also called Henry equations, tend to give lower BMR estimates. This applies to men aged 18 to 60 and to women over 18, compared with the current FAO/WHO/UNU equations ⁷.

What those sources do say is that fat-free mass (FFM) was the best single predictor of REE (R2 = 0.64), giving REE = 19.7 x FFM + 413. ¹