How to use it
- Under Units, pick Metric or US.
- Choose Sex (Male or Female), then enter Age, Height and Weight. Results update as you type.
- Optionally add Body fat %. It unlocks two lean-mass equations, Katch-McArdle and Cunningham. Coming from the body fat calculator, "Try this next" fills it in for you.
- Use Formula to pick which equation is the main result. All of them stay visible in the table.
- Open How this was calculated to see your numbers inside the equation. Keep the result with Copy link, Save image or Share.
- Tick Remember my details on this device to fill in the other calculators automatically. Forget my details clears them.
What BMR means
Basal metabolic rate (BMR) is the energy your body uses at rest to keep breathing, circulating blood and holding its temperature. It is given in kilocalories per day (kcal/day), the unit food labels call calories.
The Mifflin-St Jeor paper calls its result resting energy expenditure (REE). REE is measured under slightly less strict conditions than BMR, but calculators use the two terms for the same estimate. BMR is the starting point for total daily energy use, which the TDEE calculator builds on.
How the calculation works
Both equations use weight in kilograms, height in centimeters and age in years. US entries are converted first (1 lb = 0.45359237 kg, 1 in = 2.54 cm). The equations were fitted separately for men and women.
Mifflin-St Jeor (1990): men: 10 × weight + 6.25 × height − 5 × age + 5. Women: 10 × weight + 6.25 × height − 5 × age − 161.
Harris-Benedict, revised by Roza and Shizgal (1984): men: 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age. Women: 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age.
Two examples, both aged 30, rounded to whole kcal at the end:
| Person | Mifflin-St Jeor | Harris-Benedict (revised) |
|---|---|---|
| Man, 80 kg, 180 cm | 800 + 1,125 − 150 + 5 = 1,780 | 1,853.6 → 1,854 |
| Woman, 60 kg, 165 cm | 600 + 1,031.25 − 150 − 161 = 1,320.25 → 1,320 | 1,383.7 → 1,384 |
How accurate is this?
A 2005 systematic review (Frankenfield and colleagues, Journal of the American Dietetic Association) compared measured resting metabolic rate with four equations. Mifflin-St Jeor came closest: it predicted within 10% of the measured value for more people than the others. It still missed by more than 10% for some people, in both directions.
The lean-mass equations swap height, age and sex for fat-free mass. Cunningham fitted 500 + 22 × lean mass in 1980, using the original Harris-Benedict subjects. Katch-McArdle, 370 + 21.6 × lean mass, is the version found in exercise physiology textbooks. Both are only as good as the body fat % you type: a tape-measure estimate can be off by several points, and that error carries straight into the result.
| Equation | Uses | kcal/day |
|---|---|---|
| Mifflin-St Jeor | weight, height, age, sex | 1,780 |
| Harris-Benedict, revised | weight, height, age, sex | 1,854 |
| Katch-McArdle | lean mass (67.1 kg) | 1,820 |
| Cunningham | lean mass (67.1 kg) | 1,977 |
Mifflin-St Jeor or Harris-Benedict?
Mifflin and colleagues built their equation from 498 healthy adults aged 19 to 78, both normal-weight and obese. They measured resting energy use by indirect calorimetry. In that group, the original 1919 Harris-Benedict equations overestimated measured REE by 5%.
Roza and Shizgal refitted the Harris-Benedict equations in 1984. That revised version is the one shown here, not the 1919 original.
A 2005 systematic review in the Journal of the American Dietetic Association compared Harris-Benedict, Mifflin-St Jeor, Owen and WHO/FAO/UNU. It rated Mifflin-St Jeor the most reliable. It predicted within 10% of measured values for more people than the others, with the narrowest error range. That is why Mifflin-St Jeor is the default here and in the other calculators.
For the same person, the revised Harris-Benedict result usually comes out higher. In the examples above the gap is about 60–75 kcal/day.
What the number does and doesn't tell you
The result is an average for people with the same sex, age, height and weight. It is not a measurement of you. The 2005 review notes that noteworthy errors remain when these equations are applied to individuals.
None of the inputs describes body composition. Two people with the same weight but different muscle mass get the same estimate. The Mifflin paper found fat-free mass to be the best single predictor of REE, but it is not an input here.
The same review notes that older adults and US ethnic minorities were underrepresented when these equations were built and validated. Estimates may fit those groups less well.
The equations were made for healthy adults. They are not made for pregnancy, illness, people under 18, or other cases where a doctor or dietitian would measure energy needs directly.
Common input mistakes
Mixing units is an easy error to make. Enter height in centimeters, or in feet and inches, not in meters. With US selected, weight goes in pounds.
Small rounding of inputs barely matters. A man entering 176 lb and 5 ft 11 in instead of 80 kg and 180 cm still gets 1,780 kcal/day from Mifflin-St Jeor.
Questions
- Is BMR the number of calories I burn in a day?
- No. BMR covers rest only. Daily energy use also includes movement, exercise and digesting food. The TDEE calculator multiplies BMR by an activity factor to estimate that total.
- Why do the two formulas give different results?
- They were fitted to different groups of people decades apart, using different measuring methods. Each equation reflects the averages of its own data, so the results never match exactly.
- Does BMR change with age?
- In both equations, age has a negative coefficient. Each extra year lowers Mifflin-St Jeor by 5 kcal/day. In revised Harris-Benedict it lowers the result by 5.677 kcal/day for men and 4.330 for women, with everything else unchanged.
- Can I use my body fat percentage?
- Yes. Type it in Body fat % and the table adds Katch-McArdle and Cunningham, which work from lean mass instead of height and age. They can suit very muscular or very lean people better than weight-based equations, but only if the body fat figure itself is reasonably accurate.
- What does Remember my details store?
- Age, sex, height, weight, units and body fat % (if you enter it), saved in this browser only. Nothing is sent to a server. Forget my details deletes it, and Copy link puts the numbers after a # in the link, which browsers don't send to the server.
- Can I use the result to plan meals?
- The number is an estimate of resting energy, not a plan. The calorie calculator shows what different percentages of estimated daily energy work out to.