What Is BMR? How to Work Out Your Basal Metabolic Rate
November 9, 2026
Your basal metabolic rate (BMR) is the energy your body uses at complete rest: breathing, keeping your heart beating, holding your temperature steady and running your organs. It's measured in kilocalories a day, the same unit food labels call calories. For most people it's the largest part of the energy they use each day, even though it doesn't include any movement at all.
This guide is general information, not medical or dietary advice. If you're planning a big change to what you eat, talk to a doctor or registered dietitian.
BMR, RMR and TDEE
- BMR (basal metabolic rate) is energy used at complete rest, measured under strict conditions: after a night's sleep, fasting, lying still in a warm room.
- RMR (resting metabolic rate) is measured under looser conditions and comes out a little higher. The two terms are often used interchangeably, and the equations below predict resting energy expenditure.
- TDEE (total daily energy expenditure) adds everything else: walking, working, exercise, even digesting food. It's always higher than BMR.
How to calculate BMR
The most widely used formula is the Mifflin-St Jeor equation, published in 1990. A systematic review in 2005 found it the most reliable of the common equations for healthy adults. It uses weight in kilograms, height in centimeters and age in years:
- Men: 10 × weight + 6.25 × height − 5 × age + 5
- Women: 10 × weight + 6.25 × height − 5 × age − 161
The BMR calculator does this for you. Doing it once by hand shows what drives the number.
Worked example: stone, pounds, feet and inches
Most people in the UK know their weight in stone and pounds and their height in feet and inches, so convert those first.
Take a 35-year-old woman who weighs 10 st 7 lb and is 5 ft 5 in tall.
- Weight. 10 st 7 lb is 10 × 14 + 7 = 147 lb. Multiply by 0.45359237 to get 66.68 kg.
- Height. 5 ft 5 in is 65 inches. Multiply by 2.54 to get 165.10 cm.
- Formula. 10 × 66.68 + 6.25 × 165.10 − 5 × 35 − 161 gives 1,363 kcal a day.
The stone to kg converter and the inches to cm converter handle the first two steps.
For a US example, a 40-year-old man who weighs 180 lb (81.65 kg) and is 5 ft 10 in (177.80 cm) tall has a BMR of about 1,733 kcal a day.
What changes your BMR
The formula makes the effect of each input easy to see:
- Each extra kilogram of body weight adds 10 kcal a day.
- Each extra centimeter of height adds 6.25 kcal a day.
- Each year of age takes away 5 kcal a day.
- For the same weight, height and age, the men's result is 166 kcal higher than the women's.
What the formula can't see is body composition. Muscle uses more energy at rest than fat does, so two people with the same weight and height can have quite different real metabolic rates. The equation gives an average for people like you, not a measurement of you.
From BMR to daily calories
To estimate how much energy you use in a whole day, multiply BMR by an activity factor. For the woman in the example above, with a BMR of about 1,363 kcal:
| Activity level | Factor | Estimated daily total |
|---|---|---|
| Sedentary | 1.2 | 1,635 kcal |
| Light exercise | 1.375 | 1,874 kcal |
| Moderate exercise | 1.55 | 2,112 kcal |
| Heavy exercise | 1.725 | 2,351 kcal |
| Athlete | 1.9 | 2,589 kcal |
The TDEE calculator applies these factors, and the calorie calculator adds a target for gradual weight loss or gain. Activity factors are rough. Many people overestimate how active they are, so the sedentary or light rows are often closer to reality.
BMR for teenagers
The Mifflin-St Jeor equation was developed from measurements of 498 healthy adults aged 19 to 78. Teenagers weren't in that group, and they're still growing, which takes extra energy. A result for a 15- or 16-year-old is a rough guide at best. Teenagers shouldn't use a BMR figure to cut calories; a doctor, school nurse or dietitian can help with questions about eating and growth.
How far to trust the number
- It's a prediction. The 2005 review found Mifflin-St Jeor more likely than other equations to land within 10% of measured resting metabolism, but errors for individuals can be larger.
- Some groups were underrepresented. Older adults and U.S. ethnic minorities were underrepresented in the research behind the equation.
- It doesn't apply in some situations, such as pregnancy or illnesses that affect metabolism.
- Only a measurement removes the guesswork. Indirect calorimetry, which measures the oxygen you use, can measure resting metabolism directly.
Common mistakes
- Treating BMR as a calorie target. BMR is what you'd burn lying still all day. Eating at or below it isn't recommended without medical guidance.
- Putting pounds and inches straight into the formula. The numbers 10 and 6.25 are for kilograms and centimeters. Convert first, or the result will be far off.
- Comparing results from different equations. Other formulas, such as Harris-Benedict, give somewhat different answers for the same person. Pick one and stick with it if you're tracking changes.