TDEECalculatorKatch-McArdle Calculator
Estimate your resting burn from your lean body mass. You'll need your body fat percentage.
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Short answer
The Katch-McArdle equation estimates your resting burn (BMR) from your lean body mass: 370 + 21.6 × lean mass (kg). It's the same for men and women and doesn't use height or age. It suits lean and muscular people better than height-and-weight formulas, but it's only as good as your body fat number. Being 5 points off changes the result by about 90 calories a day for a 180 lb person.
The equation
- Lean mass = weight × (1 − body fat %)
- BMR = 370 + 21.6 × lean mass (kg)
In pounds: BMR = 370 + 9.8 × lean mass (lb). Same answer, with the conversion built in.
Worked example
A 180 lb (81.6 kg) man at 18% body fat:
| Step | Result |
|---|---|
| Lean mass: 81.6 kg × (1 − 0.18) | 67.0 kg |
| 21.6 × 67.0 kg | 1,446 |
| + 370 | 370 |
| BMR | 1,816 |
At "Moderate" activity (1.55), that's about 2,815 calories a day. The calculator above shows your own numbers worked through the formula.
Your body fat number matters most
Because body fat is the only body measurement in the formula, an error there goes straight into your result. Here's the same 180 lb man if his body fat reading were 5 points off either way:
| Body fat reading | Lean mass | BMR | TDEE at Moderate |
|---|---|---|---|
| 13% | 71.0 kg | 1,904 | 2,952 |
| 18% | 67.0 kg | 1,816 | 2,815 |
| 23% | 62.9 kg | 1,728 | 2,678 |
Each 5 points moves his BMR by about 88 calories and his daily total by about 137. That's why the athlete studies below measured body fat with lab methods such as DEXA or air displacement (BodPod). If your number came from a bathroom scale or a guess, treat the result as rough and compare it with the Mifflin-St Jeor calculator, which doesn't need body fat at all.
Where the equation comes from
The version almost every calculator uses, 370 + 21.6 × lean mass, is the general equation J.J. Cunningham proposed in 1991 after pooling earlier studies of nearly 1,500 adults, both lean and with obesity. Online it's usually called Katch-McArdle. Cunningham's earlier 1980 equation (500 + 22 × lean mass) gives higher numbers and shows up in some sports research.
The idea behind both is that fat-free mass (muscle, organs, bone and water) tracks resting burn more closely than weight does. In the study that created the Mifflin-St Jeor equation, fat-free mass alone explained 64% of the differences in resting burn between people, more than body weight (56%).
When it beats Mifflin-St Jeor
For most people the two formulas land close together. They split when someone carries a lot more or less muscle than average for their size:
| Person | Mifflin-St Jeor | Katch-McArdle |
|---|---|---|
| Man, 30, 6 ft, 200 lb, 10% body fat | 1,905 | 2,134 |
| Woman, 35, 5 ft 5 in, 160 lb, 32% body fat | 1,422 | 1,436 |
| Man, 45, 5 ft 10 in, 260 lb, 35% body fat | 2,071 | 2,026 |
| Woman, 60, 5 ft 4 in, 140 lb, 38% body fat | 1,190 | 1,220 |
The lean, muscular man is the case where a height-and-weight formula struggles, and the research backs that up. In 90 recreational athletes with body fat measured by BodPod, Cunningham's older 1980 lean-mass equation was within 10% of measured resting burn for 85% of the men and 78% of the women; Mifflin-St Jeor managed fewer than half. A 2023 review of 29 studies in athletes (1,430 people) found the average estimate from the 1991 equation didn't differ from measured resting burn, while Mifflin-St Jeor's did.
It isn't perfect for athletes either. In a 2018 study of college athletes, all five equations tested came in low on average, and the review found big differences from study to study. Treat any formula as a first guess.
When to skip it
- You don't have a body fat number you trust. Use Mifflin-St Jeor instead.
- You're pregnant. In one study, fat mass rather than lean mass predicted resting burn in pregnant women, the opposite of the usual pattern. Talk to your doctor or midwife about calorie needs.
- You're under 18. Our calculators are for adults aged 18 to 80.
Common questions
Is Katch-McArdle more accurate than Mifflin-St Jeor?
For lean, muscular people with a good body fat measurement, usually yes. For everyone else the two land close together, and Mifflin-St Jeor doesn't depend on a body fat reading that could be off.
Why doesn't the formula use my age, height or sex?
Lean mass already carries most of what those numbers stand in for. (The calculator still asks for them to work out your macros and the rest of your results.) Bigger, younger and male bodies tend to have more of it, and lean mass is what burns most of your resting calories.
What's the best way to measure body fat?
The studies behind lean-mass formulas used lab methods such as DEXA or a BodPod. Calipers from an experienced tester are a cheaper option. Whatever you use, stick with the same method so changes over time mean something.
Is Katch-McArdle the same as the Cunningham equation?
The 370 + 21.6 × lean mass version is Cunningham's 1991 equation. His 1980 version, 500 + 22 × lean mass, gives higher numbers for the same person.
More calculators
Not medical advice. These numbers are estimates for healthy adults aged 18–80, based on published equations. They aren't reviewed by a doctor or registered dietitian. Talk to one before making big changes to how you eat, especially if you're pregnant or breastfeeding, under 18, have a history of disordered eating, have a medical condition, or take medication that affects appetite or weight. Medical disclaimer
Written by Peter Kohout, strength & conditioning coach
Sources
- Cunningham JJ. Body composition as a determinant of energy expenditure: a synthetic review and a proposed general prediction equation. Am J Clin Nutr, 1991.
- Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. Am J Clin Nutr, 1980.
- Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990.
- ten Haaf T, Weijs PJM. Resting energy expenditure prediction in recreational athletes of 18–35 years. PLoS One, 2014.
- O'Neill JER, Corish CA, Horner K. Accuracy of resting metabolic rate prediction equations in athletes: a systematic review with meta-analysis. Sports Med, 2023.
- Jagim AR, Camic CL, Kisiolek J, et al. Accuracy of resting metabolic rate prediction equations in athletes. J Strength Cond Res, 2018.
- Bronstein MN, Mak RP, King JC. Unexpected relationship between fat mass and basal metabolic rate in pregnant women. Br J Nutr, 1996.
You're a 30-year-old man, 5 ft 10 in and 180 lb, moderately active.
You burn about
2,763
calories a day
Likely range 2,490–3,040 · 19,341 a week
This already counts your workouts, so don't add your watch's exercise calories on top.
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