BMR Calculator: Basal Metabolic Rate, 3 Equations
Estimate your basal metabolic rate, the calories your body burns at rest, with the Mifflin-St Jeor, revised Harris-Benedict and Katch-McArdle equations side by side, in kcal or kJ, metric or US units. Nothing is sent anywhere.
Enter your age, height and weight to see your calories.
About the BMR Calculator
The BMR Calculator estimates your basal metabolic rate: the energy your body uses in a day at complete rest, just to keep your heart beating, your lungs breathing, your brain working and your body warm. For most people it is the largest part of daily energy use, typically 60 to 70 percent of the total, before any walking, exercise or digestion is added.
Enter your age, sex, height and weight, in metric or US customary units, and the calculator shows your BMR by the equation you choose, with all three equations side by side so you can see how far they agree. Add a body fat percentage and you also see your lean body mass and the Katch-McArdle estimate. Results can be read in kilocalories or kilojoules.
Nothing is uploaded; the calculation runs in your browser and your measurements never leave your device.
This is an estimate, not medical advice. A predicted BMR is the average for people with your measurements; your measured value can be 10 percent higher or lower. Thyroid conditions, some medicines, pregnancy and illness all change it.
BMR and resting metabolic rate
Strictly, BMR is measured in a laboratory after an overnight fast, lying still in a warm room just after waking. Resting metabolic rate (RMR), or resting energy expenditure, is measured under looser conditions and comes out a little higher. The Mifflin-St Jeor equation was in fact fitted to resting energy expenditure, but the two terms are used interchangeably in everyday use, and in this calculator.
The three equations
Mifflin-St Jeor
Published in 1990 from measurements of 498 healthy adults. For men, ; for women, the constant is −161 instead of +5. Weight is in kilograms, height in centimetres and age in years. It is the default because reviews have found it the most accurate of the common equations for most adults.
Revised Harris-Benedict
The 1919 Harris-Benedict equation, refitted by Roza and Shizgal in 1984. For men, ; for women, . It tends to give a slightly higher figure than Mifflin-St Jeor.
Katch-McArdle
lean body mass in kilograms, where lean mass is weight minus fat mass. Because muscle uses more energy than fat, this equation suits lean or muscular people whose body fat percentage is known.
Worked example
A 30-year-old woman, 165 cm tall and weighing 60 kg, has a Mifflin-St Jeor BMR of 10 × 60 + 6.25 × 165 − 5 × 30 − 161 = 1,320 kcal a day. The revised Harris-Benedict equation gives about 1,384 kcal for the same woman.
From BMR to daily calories
BMR does not include any movement, so it is not the amount to eat. Multiply it by an activity factor to get your maintenance calories: the TDEE Calculator shows every level, and the full Calorie Calculator adds goals for weight loss and gain. The BMI Calculator puts your weight in context, and the Mass Converter turns pounds into kilograms.
Sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 1990;51(2):241–247.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. American Journal of Clinical Nutrition 1984;40(1):168–182.
- McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. Lippincott Williams & Wilkins.
Open-source credits
The calculations are implemented in-house in TypeScript, with no third-party libraries, and follow the published Mifflin-St Jeor, revised Harris-Benedict and Katch-McArdle equations.