UNDERSTAND THE METHOD
How to use this calculator
Enter an adult profile. Compare the standard equations or add body composition. A measured body-fat result and a BMI estimate have different uncertainty. Resting energy does not include all daily activity.
What the result can tell you
These equations estimate resting expenditure. Indirect calorimetry measures it. Cunningham 1991 uses 370 + 21.6 × fat-free mass, the equation studies call Katch–McArdle. Cunningham 1980 uses 500 + 22 × lean body mass. The result labels show both equations separately.
Resting energy by body weight and fat-free mass
Resting energy is the energy your body uses at rest, before food and activity are added. This calculator's standard estimate is the Mifflin–St Jeor equation, which was built from resting energy measured by indirect calorimetry in 498 healthy adults aged 19 to 78. It also shows the revised Harris–Benedict equation. Both use weight, height, age and sex. The tables below run both equations for two example adults aged 40. They are examples, not averages or targets.
Woman, 163 cm, age 40: resting kcal per day
| Body weight | Mifflin–St Jeor | Revised Harris–Benedict |
|---|---|---|
| 50 kg (110 lb) | 1,160 | 1,242 |
| 60 kg (132 lb) | 1,260 | 1,334 |
| 70 kg (154 lb) | 1,360 | 1,427 |
| 80 kg (176 lb) | 1,460 | 1,519 |
| 90 kg (198 lb) | 1,560 | 1,612 |
| 100 kg (220 lb) | 1,660 | 1,704 |
| 110 kg (243 lb) | 1,760 | 1,797 |
Man, 178 cm, age 40: resting kcal per day
| Body weight | Mifflin–St Jeor | Revised Harris–Benedict |
|---|---|---|
| 50 kg (110 lb) | 1,420 | 1,385 |
| 60 kg (132 lb) | 1,520 | 1,519 |
| 70 kg (154 lb) | 1,620 | 1,653 |
| 80 kg (176 lb) | 1,720 | 1,787 |
| 90 kg (198 lb) | 1,820 | 1,921 |
| 100 kg (220 lb) | 1,920 | 2,055 |
| 110 kg (243 lb) | 2,020 | 2,189 |
In Mifflin–St Jeor, each extra kilogram adds 9.99 kcal a day, each extra centimeter of height adds 6.25 kcal and each extra year of age takes away 4.92 kcal, for men and women alike. At the same weight, height and age, the equation puts men 166 kcal a day above women.
If you know your body fat percentage, for example from a DEXA scan, choose Known body fat above. The calculator works out fat-free mass as weight × (1 − body fat %) and also runs Cunningham's equations, which use fat-free mass alone, with no weight, height, age or sex.
Studies call 370 + 21.6 × fat-free mass in kg the Katch–McArdle equation. It is the same arithmetic as Cunningham's 1991 equation, so the 370 + 21.6 row in the result above, shown once you add body composition, is the Katch–McArdle result. The 500 + 22 × kg equation from Cunningham's 1980 paper is a different equation and gives a higher number. At 60 kg of fat-free mass, Katch–McArdle gives 1,666 kcal a day and Cunningham 1980 gives 1,820, 154 kcal apart. The gap grows by 0.4 kcal for each extra kilogram of fat-free mass.
Resting kcal per day by fat-free mass
| Fat-free mass | Katch–McArdle (Cunningham 1991): 370 + 21.6 × kg | Cunningham 1980: 500 + 22 × kg |
|---|---|---|
| 40 kg (88 lb) | 1,234 | 1,380 |
| 45 kg (99 lb) | 1,342 | 1,490 |
| 50 kg (110 lb) | 1,450 | 1,600 |
| 55 kg (121 lb) | 1,558 | 1,710 |
| 60 kg (132 lb) | 1,666 | 1,820 |
| 65 kg (143 lb) | 1,774 | 1,930 |
| 70 kg (154 lb) | 1,882 | 2,040 |
| 75 kg (165 lb) | 1,990 | 2,150 |
| 80 kg (176 lb) | 2,098 | 2,260 |
Example: a person who weighs 80 kg at 20% body fat has 64 kg of fat-free mass. Cunningham 1991 gives 370 + 21.6 × 64 = 1,752 kcal a day, and Cunningham 1980 gives 1,908 kcal a day.
These equations predict averages for groups of people, so your own resting energy can be higher or lower. Indirect calorimetry measures it. Working backward from a measured resting energy to a body-fat percentage would carry the full error of these group equations.
Common questions
What does the RMR result include?
It estimates resting energy expenditure. Resting energy does not include all daily activity, and indirect calorimetry is the measurement method described by the source.
Why does the calculator ask for a body-composition source?
You can use a measured body-fat result, a BMI-based estimate, or standard equations. A BMI-based body-fat input has different uncertainty, and the Cunningham equations are shown separately.
Is this a Katch–McArdle calculator?
Yes, once you add body composition. Published studies, such as Xu and colleagues (Frontiers in Nutrition, 2026), call 370 + 21.6 × fat-free mass in kg the Katch–McArdle equation. Its arithmetic is the same as the equation Cunningham proposed in 1991 (American Journal of Clinical Nutrition), which this calculator shows. Cunningham's 1980 equation, 500 + 22 × kg, is a different equation and gives a higher number. The result shows both.
What is a resting metabolic rate test, and is it more accurate than a calculator?
An RMR test measures your resting energy by indirect calorimetry instead of predicting it from weight, height, age and sex. Before the test you avoid food, alcohol, caffeine, nicotine and exercise for some hours, then rest for 10 to 20 minutes. A 2006 review of test methods found that a 10-minute measurement, with the first 5 minutes dropped and the last 5 varying by less than 10%, gave an accurate reading. A test run that way measures you directly, so it removes the prediction error of an equation, though the test itself still has some measurement error. A 2005 review found Mifflin–St Jeor, the standard estimate here, came within 10% of measured RMR for more people than the other common equations, but it still made noteworthy errors for some individuals, and older adults and US ethnic minorities were underrepresented in the studies.
Can I work out my body fat from a measured RMR?
Only roughly. Rearranging the Katch–McArdle equation gives fat-free mass in kg = (RMR − 370) ÷ 21.6, and fat mass is your weight minus that. For an 80 kg person with a measured RMR of 1,700 kcal, that is 61.6 kg fat-free mass and 18.4 kg fat, or 23.0% body fat. But every 100 kcal of RMR moves fat-free mass by about 4.6 kg: at 1,600 or 1,800 kcal the same person comes out at 28.8% or 17.2%. The equation was fitted to predict RMR from body composition, not the reverse, so a body fat measurement is the better input here.
Sources & limitations10 sources
Sources checked September 12, 2026. These notes identify methods and assumptions. They have not received an independent clinical review.
- Review of resting energy by age, sex category, and BMI. Confidence intervals describe group means.pubmed.ncbi.nlm.nih.gov
- Mifflin–St Jeor resting energy equation.pubmed.ncbi.nlm.nih.gov
- Revised Harris–Benedict coefficients.pubmed.ncbi.nlm.nih.gov
- Cunningham 1980 proposes 500 + 22 × lean body mass.pubmed.ncbi.nlm.nih.gov
- Fat-free mass and resting metabolic rate.pubmed.ncbi.nlm.nih.gov
- Lists Katch–McArdle as 370 + 21.6 × fat-free mass, separate from Cunningham 500 + 22.pmc.ncbi.nlm.nih.gov
- Uses the Katch–McArdle formula, 370 + 21.6 × lean body mass in kg.pmc.ncbi.nlm.nih.gov
- HERITAGE body-fat estimates and population differences.pubmed.ncbi.nlm.nih.gov
- Systematic review: Mifflin–St Jeor predicted resting energy within 10% of measured in more adults than other common equations, with noteworthy individual errors.pubmed.ncbi.nlm.nih.gov
- Systematic review of the conditions and test length for measuring resting metabolic rate by indirect calorimetry.pubmed.ncbi.nlm.nih.gov