BMR Calculator

BMR is basal metabolic rate, the energy your body uses at rest for breathing, circulation and keeping warm. The tool uses the Mifflin-St Jeor equation, and it also shows the revised Harris-Benedict result so you can compare the two.

Formulas

How it works, step by step

1. First, the calculator converts your height and weight to centimeters and kilograms.
2. Then it applies both equations for your sex and age.
3. Finally, it shows the Mifflin-St Jeor value as your headline, rounded to the nearest 10 calories.

Worked example

For a 30-year-old man who is 180 cm tall and weighs 80 kg, Mifflin-St Jeor gives 1,780 calories a day. The revised Harris-Benedict equation also gives about 1,854, which comes to roughly 4% more.

Accuracy and limits

Mifflin and colleagues measured resting energy use in 498 healthy adults and fitted their equation to the data. In that group, the original 1919 Harris-Benedict equations still overestimated measured values by 5%.

Roza and Shizgal revised the Harris-Benedict equations in 1984, and they reported a precision of plus or minus 14% for normally nourished people. Meanwhile, a 2005 systematic review found that Mifflin-St Jeor landed within 10% of measured rate for more people than the other common equations.

The reference standard is a lab test called indirect calorimetry, which measures the oxygen you use at rest. Because that test needs equipment, most people rely on an equation instead.

• BMR covers rest only. Since a normal day burns more, use the TDEE calculator for meal planning.
• In the original study, fat-free mass was the best single predictor of resting burn, but this equation leaves it out.
• The studies included few older adults, so treat results for that group with extra caution.

Sources

1. Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. Used for: The Mifflin-St Jeor equation and the 498 adults it came from.
2. Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182. Used for: The revised Harris-Benedict equation and its stated precision.
3. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789. Used for: How often each common equation lands within 10% of measured resting rate.

Sources and math last reviewed: November 4, 2026.