BMR Calculator

What is basal metabolic rate?

Basal metabolic rate (BMR) is the energy your body uses in a day for its basic work, such as keeping the heart and breathing muscles going, holding body temperature and running the brain, while you lie awake and completely at rest. This calculator estimates yours with the Mifflin–St Jeor equation, works out the same estimate with three other published equations, and marks the ±10% band that studies use to judge whether an estimate is accurate. Results are in kilocalories (kcal), the calories used in nutrition, and in kilojoules (kJ) a day.

In a lab, BMR is measured awake and lying down, 10 to 12 hours after the last meal, after 8 hours of physical rest, relaxed, in a room neither warm enough to sweat nor cool enough to shiver. Nobody lives in those conditions, which is why the number is a baseline, not a day’s total.

How to use it

• Units: US (feet, inches and pounds), metric (centimeters and kilograms) or UK (feet, inches, stones and pounds). Switching carries your height and weight into the new units, and the line under each box shows the entry in other units.
• Sex used by the equation: Mifflin–St Jeor, Harris–Benedict and Schofield each have a male and a female version. This choice only picks the version; the questions at the end cover what to do if neither fits.
• Height and weight: height without shoes, weight in light clothing.
• Age: in whole years, from 18 to 100. The equations were built from adults, and a note appears outside the ages Mifflin and St Jeor studied.
• Body fat (optional): a percentage from a body-composition scan, a skinfold test or a bioimpedance scale. With it, the table adds Katch–McArdle, which works from lean mass instead of weight. Leave it blank if you don’t have a reading rather than guessing.

Results change as you type. The Try buttons load the cases in the table further down. Your measurements go into a share link only if you press Share link and accept the notice.

BMR formulas: Mifflin–St Jeor, Harris–Benedict and Katch–McArdle

With weight $W$ in kilograms, height $H$ in centimeters, age $A$ in years and lean body mass $L$ in kilograms, each equation gives kcal a day:

• $W$: pounds × 0.45359237, or stones × 14 + pounds first.
• $H$: inches × 2.54 (feet × 12 + inches first).
• $A$: whole years.
• $L$: the part of your weight that isn’t fat.

Schofield’s equations, which the FAO/WHO/UNU expert report kept for estimating energy needs, use weight alone, with one equation per sex and age band:

Mifflin and St Jeor fitted their equation to 498 healthy adults aged 19 to 78 in 1990. The paper printed 9.99, 6.25 and 4.92 as coefficients and 166 kcal between the sexes, then gave the rounded forms above as equally good. This calculator uses the rounded forms. The revised Harris–Benedict equations are Roza and Shizgal’s 1984 refit of the 1919 originals with more subjects over a wider age range. Katch–McArdle comes from McArdle, Katch and Katch’s exercise physiology textbook.

Worked example: 5 ft 6 in, 165 lb, age 52, 34% body fat

The example uses the female equation.

1. Convert to metric: 165 lb × 0.45359237 = 74.843 kg, and 5 ft 6 in = 66 in × 2.54 = 167.64 cm.
2. Mifflin–St Jeor: 10 × 74.843 + 6.25 × 167.64 − 5 × 52 − 161 = 748.43 + 1,047.75 − 260 − 161 = 1,375.18, shown as 1,375 kcal a day.
3. In kilojoules: 1,375.18 × 4.184 = 5,753.74, about 5,754 kJ a day.
4. Per hour: 1,375.18 ÷ 24 = 57.30, about 57 kcal.
5. The ±10% band: 1,375.18 × 0.9 = 1,237.66 and 1,375.18 × 1.1 = 1,512.70, so 1,238 to 1,513 kcal.
6. Revised Harris–Benedict: 447.593 + 9.247 × 74.843 + 3.098 × 167.64 − 4.330 × 52 = 447.593 + 692.07 + 519.35 − 225.16 = 1,433.85, shown as 1,434 kcal: 59 more (+4.3%).
7. Katch–McArdle: lean mass 74.843 × (1 − 0.34) = 49.396 kg; 370 + 21.6 × 49.396 = 1,436.96, shown as 1,437 kcal: 62 more (+4.5%).
8. Schofield for women 30 to 59: 8.126 × 74.843 + 845.6 = 1,453.77, shown as 1,454 kcal: 79 more (+5.7%).

The four estimates span 79 kcal, from 1,375 to 1,454, and all sit inside the ±10% band. The equations disagree with each other by far less than any one of them can miss for an individual.

Which BMR formula is most accurate?

For most adults, Mifflin–St Jeor. A 2005 systematic review in the Journal of the American Dietetic Association found it predicted resting metabolic rate within 10% of the measured value in more people, both nonobese and obese, than Harris–Benedict or the other common equations, and with the narrowest range of errors. That is why it is the headline here. Mifflin’s own paper found that the 1919 Harris–Benedict equations overestimated measured values by 5%, and the revised version also comes out higher than Mifflin–St Jeor for most adult sizes and ages: 4.3% higher in the example.

Katch–McArdle can do better when you have a good body-fat measurement, because in Mifflin and St Jeor’s own data, lean mass alone predicted resting energy use more closely than weight alone did. In a 2021 study of 620 women it had the highest share of estimates within 10% (39.5%), and among stroke survivors it overestimated least. It is only as accurate as the body-fat reading, though; the what-if table shows how far a few points move it.

How accurate is a BMR estimate for one person?

Treat any estimate as good to about 10% at best, and sometimes worse. The published checks:

• The 2005 review judged Mifflin–St Jeor the most reliable but still found noteworthy errors for individuals, and few older adults or US ethnic minorities in the studies.
• Roza and Shizgal put the precision of the Harris–Benedict equations at about ±14% for normally nourished people, and their refit with more subjects came out much the same.
• In the 2021 study of healthy Chilean women, every equation tended to overestimate. Mifflin–St Jeor averaged 1,390 kcal against a measured average of 1,183 and was within 10% for only 33% of the women.
• The FAO/WHO/UNU table lists Schofield’s standard errors as 108 to 167 kcal a day, depending on sex and age.

In the example, the ±10% band runs from 1,238 to 1,513 kcal, a range of 275 kcal, while the four equations sit within 79 kcal of each other. Only a measurement by indirect calorimetry, the lab method the equations were fitted to, gives your own number.

BMR vs RMR vs TDEE

BMR and RMR (resting metabolic rate, also called resting energy expenditure) both describe energy use at rest; BMR has the stricter lab definition above. Mifflin–St Jeor and the revised Harris–Benedict equations were fitted to resting measurements (both papers speak of resting energy expenditure), so for a calculator, BMR and RMR are the same estimate.

TDEE, total daily energy expenditure, is everything you burn in a day, activity included. The FAO/WHO/UNU report puts BMR at about 45 to 70% of an adult’s total. To estimate that total, multiply BMR by an activity level in a TDEE calculator; this page stops at BMR on purpose, and Continue in the TDEE Calculator under the results carries your height, weight, age and sex there.

How many calories do you burn at rest?

About your BMR divided by 24 each hour: 57 kcal (240 kJ) in the example. For sleep, the FAO/WHO/UNU report counts each hour asleep at 1.0 × BMR when it adds up a day’s energy, so the same per-hour figure serves for a night: 8 hours at the example’s rate is 8 × 57.30 = 458 kcal.

What affects your BMR

Mostly sex, body size, body composition and age, and the equations show each one’s size:

• Weight: Mifflin–St Jeor adds 10 kcal a day per kilogram, about 4.5 per pound. The example at 155 lb instead of 165 lb gives 1,330 kcal, 45 less.
• Height: 6.25 kcal per centimeter, about 15.9 per inch.
• Age: 5 kcal less each year in Mifflin–St Jeor, 50 per decade. Revised Harris–Benedict takes 5.677 a year for men and 4.330 for women.
• Sex constant: the male result is 166 kcal higher at the same size and age.
• Lean mass: each kilogram of lean mass adds 21.6 kcal in Katch–McArdle, which has no age term at all.

These cases are on the Try buttons (kcal a day; ”—” means no body fat was entered):

The lean man’s Katch–McArdle estimate is 7.4% above Mifflin–St Jeor: 88% of his weight is lean mass, and Katch–McArdle counts only that. At 84, Mifflin–St Jeor falls by 160 kcal (32 years × 5), Katch–McArdle doesn’t move, and Schofield switches to its 60-and-over equation; both end up outside the ±10% band, and a note says the age is beyond Mifflin’s sample.

Reading the result

• Headline: Mifflin–St Jeor in kcal and kJ a day, with the inputs it used.
• ±10% band, per hour and across the equations: the accuracy band around the headline, BMR ÷ 24, and the lowest and highest of the estimates with the gap between them.
• Your BMR by equation: each equation’s estimate, its difference from Mifflin–St Jeor and whether it lands inside the band. Download CSV saves it.
• Each estimate against the ±10% band: the same numbers on a scale from 25% below to 25% above the headline, with what each equation works from, which is why they differ.
• How this was calculated: every conversion and equation with your numbers in it.
• BMR at other weights: your height, age and sex with the weight 10 and 20 lb (5 and 10 kg, or 1 and 2 stone) either side.
• Katch–McArdle at other body-fat readings: shown when you enter body fat. In the example, a reading 5 points lower gives 1,518 kcal and 5 points higher 1,356, 81 kcal either way.

Save for comparison keeps up to three results side by side with the change from the first, which helps when you compare two body-fat readings or before-and-after weights.

Assumptions and limitations

• The equations describe healthy adults. None has an input for pregnancy, breastfeeding, illness, fever, medicines or a recent diet; among survivors of chronic stroke, for example, every equation overestimated.
• Mifflin–St Jeor’s sample was 19 to 78 years old. At 18 or from 79 the page still calculates and says the age is outside that range.
• Schofield changes equation at 30 and 60, so its estimate jumps: for a 70 kg woman it is 1,524 kcal at 29 and 1,414 at 30.
• Katch–McArdle assumes the body-fat reading is right. At the example weight each percentage point is worth 16.2 kcal a day.
• Results are rounded to the whole kcal for display. The differences in the tables are between the rounded numbers, so they add up as shown.
• This is an estimate for general information, not a measurement or medical advice.

Common mistakes

• Treating BMR as a calorie target. It is the energy for a day of lying still, not what you use on a normal day.
• Typing kilograms into the pounds box. A 52-year-old woman of 5 ft 6 in and 75 kg who types 75 into the pounds box gets 967 kcal instead of 1,377, because 75 lb is only 34.02 kg. The calculator warns that a BMI of 12.1 is very rare; choose Metric instead.
• Guessing body fat. A reading off by 5 points moves Katch–McArdle by 81 kcal at the example weight. Without a measurement, leave the box empty.
• Comparing calculators without checking the equation. A tool using Harris–Benedict will often show a few percent more than one using Mifflin–St Jeor for the same person.
• Reading the result as exact. Whole-calorie results look precise, but the ±10% band is the honest size of the uncertainty.