Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle for BMR
Basal metabolic rate (BMR) is the energy your body uses just to stay alive: powering the heart, lungs, brain and the rest of the machinery while you are at rest. Almost every calorie target starts from it, but there is no single BMR formula. Several equations are in common use, and each gives a slightly different answer.
This article puts three popular ones side by side, runs the same person through all of them, and explains how to choose. BMR here is measured in kilocalories (kcal) per day; multiply by 4.184 to convert to kilojoules.
What BMR measures
True BMR is measured under strict conditions: awake but fully rested, after a fast, in a comfortably warm room. Those conditions are hard to reproduce, so many studies and calculators report resting metabolic rate (RMR) instead, which is measured under looser conditions and is usually a little higher. In practice the two terms are often used interchangeably, and the RMR calculator and BMR calculator give similar figures.
Whichever name is used, the number is not your total daily energy use. It excludes movement, exercise and digesting food. The next step, multiplying by an activity factor, is covered in the guide to choosing an activity multiplier.
The three equations
In all three, weight (W) is in kilograms, height (H) is in centimetres, age (A) is in years, and the result is kcal per day.
Mifflin-St Jeor was published in 1990 using data from modern adults:
Men: 10 × W + 6.25 × H − 5 × A + 5
Women: 10 × W + 6.25 × H − 5 × A − 161
Harris-Benedict dates from the early twentieth century. The version below is the 1984 revision of the original:
Men: 88.362 + 13.397 × W + 4.799 × H − 5.677 × A
Women: 447.593 + 9.247 × W + 3.098 × H − 4.330 × A
Katch-McArdle ignores height, age and sex. It uses lean body mass (LBM), which is body weight minus fat, in kilograms:
BMR = 370 + 21.6 × LBM
The first two predict from weight, height and age. Katch-McArdle depends on knowing your body fat, which you could estimate with a tape-measure method or the lean body mass calculator.
One person, three answers
A man, 35 years old, 80 kg, 180 cm, about 20% body fat.
- Mifflin-St Jeor: 10 × 80 + 6.25 × 180 − 5 × 35 + 5 = 800 + 1,125 − 175 + 5 = 1,755 kcal.
- Harris-Benedict (revised): 88.362 + 13.397 × 80 + 4.799 × 180 − 5.677 × 35 = 88.362 + 1,071.76 + 863.82 − 198.695 = 1,825 kcal.
- Katch-McArdle: lean mass is 80 × 0.80 = 64 kg, so 370 + 21.6 × 64 = 1,752 kcal.
A woman, 40 years old, 65 kg, 165 cm, about 30% body fat. Mifflin-St Jeor gives 650 + 1,031.25 − 200 − 161 = 1,320 kcal. Harris-Benedict gives 1,387 kcal. Her lean mass is 65 × 0.70 = 45.5 kg, so Katch-McArdle gives 370 + 21.6 × 45.5 = 1,353 kcal.
| Person | Mifflin-St Jeor | Harris-Benedict | Katch-McArdle |
|---|---|---|---|
| Man, 35, 80 kg, 180 cm | 1,755 | 1,825 | 1,752 |
| Woman, 40, 65 kg, 165 cm | 1,320 | 1,387 | 1,353 |
The spread is about 70 kcal a day, around 4 to 5%. That is small compared with the uncertainty in the next step, but it shows that no formula gives a precise figure.
Which one should you use?
- Mifflin-St Jeor is a sensible default for most healthy adults. Published comparisons of prediction equations have generally rated it among the more reliable, and it only needs numbers everyone knows.
- Harris-Benedict is the classic, and many older guides still use it. In this example it reads higher than the other two, and it was built on data from an earlier era.
- Katch-McArdle can be a better fit for very lean or very muscular people, whose weight and height alone understate their lean mass. Its weakness is its input: an error in your body fat estimate flows straight through. Being 5 percentage points off on an 80 kg person shifts lean mass by 4 kg and BMR by about 86 kcal.
Whatever you choose, treat it as an estimate. Equations describe an average across many people, so your own BMR can sit above or below the prediction. Direct measurement needs a lab technique called indirect calorimetry.
This article is general education and not medical advice. If you are planning a major change in eating or have a medical condition, ask a doctor or registered dietitian for personalised guidance.
- BMR Calculator: Enter your age, sex, height and weight to estimate how many calories your body burns at complete rest. The guide below explains the equation, shows how to scale the result for activity and lists what moves BMR up or down.
- Resting Metabolic Rate Calculator: Enter your age, sex, height and weight to estimate how many calories your body burns at rest in a day. Two well-known equations are shown side by side so you can see how far they agree.
- Lean Body Mass Calculator: Enter your weight, height and a few tape measurements to estimate how much of your body is lean tissue. The guide shows the Navy formulas, a worked example and how to read the lean mass index.
This article is general information, not professional advice. See our Disclaimer and Editorial Policy.
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