How to use the lean body mass calculator
- Pick Male or Female, because each formula has separate numbers.
- Choose Metric (kg, cm) or US (lb, ft, in). What you typed converts when you switch.
- Enter your Weight and Height. Results update as you type.
- Read the average lean body mass, the three formula results, and the fat mass, body fat and BMR estimates below it.
How lean body mass is calculated
Each formula estimates lean mass from weight (W, in kg) and height (H, in cm):
- Boer (1984): men 0.407 W + 0.267 H − 19.2, women 0.252 W + 0.473 H − 48.3.
- James (1976): men 1.10 W − 128 (W ÷ H)², women 1.07 W − 148 (W ÷ H)².
- Hume (1966): men 0.3281 W + 0.33929 H − 29.5336, women 0.29569 W + 0.41813 H − 43.2933.
The headline is the average of the formulas. James drops out of it at a BMI of 35 or higher, because its squared term plateaus near a BMI of 37 for women and 43 for men and then falls as weight rises. Fat mass is weight minus that average, body fat is fat mass divided by weight, and BMR is the Katch-McArdle equation, 370 + 21.6 × lean mass in kg.
Worked example
With the starting inputs (male, 75 kg, 175 cm), Boer gives 0.407 × 75 + 0.267 × 175 − 19.2 = 58.1 kg, James gives 1.10 × 75 − 128 × (75 ÷ 175)² = 59.0 kg, and Hume gives 0.3281 × 75 + 0.33929 × 175 − 29.5336 = 54.4 kg. Their average is 57.2 kg (126.0 lb). Fat mass is 75 − 57.2 = 17.8 kg, body fat is 23.8%, and BMR is 370 + 21.6 × 57.2 = 1,605 kcal per day.
Limits and edge cases
These formulas are for adults and see only height, weight and sex, so a lifter and an inactive person with the same numbers get the same result. Treat the body fat figure as a rough guide: the body fat calculator or a DEXA scan gets closer. The calculator accepts 20 to 400 kg (45 to 880 lb) and 100 to 250 cm (3 ft 4 in to 8 ft 2 in), shows N/A for any formula whose answer is not between zero and your body weight, and notes a BMI under 15 or over 50. For daily targets, use the calorie calculator and macro calculator.
Frequently asked questions
How do I calculate lean body mass?
Subtract your fat mass from your body weight, or estimate it from height and weight with a formula such as Boer, listed above. A DEXA scan measures it directly.
Which lean body mass formula is most accurate?
None is best for everyone. Boer and Hume keep rising as weight rises, while James levels off near a BMI of 37 for women and 43 for men and then falls, so it underestimates in heavier bodies. That is why this calculator averages the formulas and drops James at a BMI of 35 or higher.
How much protein do I need for my lean body mass?
Studies count protein per kilogram of body weight, not lean mass. A 2018 meta-analysis found no extra muscle gain in weight trainers above about 1.6 g per kg of body weight per day, which is 120 g a day at 75 kg. Dividing by lean mass is a common shortcut, but it is not what those studies measured.
Can I use these results to dose a medication?
No. Doctors set drug doses by protocol, and some protocols use other lean weight formulas. Use this page for general information only.
Sources: Boer, Am J Physiol 1984; James, Research on Obesity, HMSO 1976; Hume, J Clin Pathol 1966; BioMed Res Int 2018; Morton et al., Br J Sports Med 2018; McArdle, Katch and Katch, Exercise Physiology (Katch-McArdle BMR).