Lean Body Mass Calculator
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Results
Estimated lean body mass 136 lb (Boer formula), with James 138 lb and Hume 127 lb, for 180 lb at 5 ft 10 in.
| Formula | Lean mass | Fat mass | Body fat |
|---|---|---|---|
| Boer (1984) | 136 lb | 44 lb | 24.7% |
| James (1976) | 138 lb | 42 lb | 23.1% |
| Hume (1966) | 127 lb | 53 lb | 29.5% |
Height-and-weight formulas assume typical muscle for your size. They can’t see whether extra weight is muscle or fat, so very muscular people get an underestimate.
This is an estimate from a published formula, not medical advice. Talk to a doctor or registered dietitian about your own situation.
How to use the lean body mass calculator
- Choose female or male and enter your age. Under 14, the children's formula is used automatically.
- Enter height and weight in feet, inches and pounds, or centimeters and kilograms.
- Compare the three adult estimates and the body fat each implies. The spread between them is a fair guide to the uncertainty.
Lean body mass formulas
James (1976): men 1.1W − 128(W ÷ H)² · women 1.07W − 148(W ÷ H)²
Hume (1966): men 0.32810W + 0.33929H − 29.5336 · women 0.29569W + 0.41813H − 43.2933
Peters (2011, children): 3.8 × 0.02154 × W^0.6469 × H^0.7236
W = weight in kg, H = height in cm, results in kg · implied body fat = (1 − LBM ÷ W) × 100
All three adult formulas come from small studies. Hume derived his from total body water measured in 56 adults; Boer proposed his in a 1984 study of body fluid volumes in healthy volunteers; the James formula comes from a 1976 UK government report on obesity. For children, A. Michael Peters and colleagues multiplied an estimate of extracellular fluid volume from height and weight (Bird and others, 2003) by 3.8, the ratio of estimated lean mass to measured extracellular volume they found in adults.
Worked example
A man 5 ft 10 in tall (177.8 cm) who weighs 180 lb (81.6 kg). Boer gives 0.407 × 81.6 + 0.267 × 177.8 − 19.2 = 61.5 kg, or 135.6 lb of lean mass, implying 24.7% body fat. James gives 138.5 lb (23.1%) and Hume 126.9 lb (29.5%). For a child of 30 kg and 138 cm, Peters gives 3.8 × 6.87 L = 26.1 kg.
How the formulas compare
Generated with the calculator's engine: lean mass, with the body fat it implies in brackets.
| Person | Boer | James | Hume |
|---|---|---|---|
| Woman, 5 ft 4 in, 130 lb | 96 lb (26%) | 96 lb (26%) | 93 lb (29%) |
| Woman, 5 ft 6 in, 170 lb | 111 lb (35%) | 113 lb (34%) | 109 lb (36%) |
| Man, 5 ft 10 in, 180 lb | 136 lb (25%) | 138 lb (23%) | 127 lb (29%) |
| Man, 6 ft 0 in, 220 lb | 155 lb (30%) | 158 lb (28%) | 144 lb (35%) |
Hume usually gives the lowest lean mass and James the highest, until BMI gets high. The James formula reaches its maximum at a BMI of about 43 for men and 36 for women; above that, it says lean mass falls as weight rises, which is not realistic, so the calculator warns you.
Getting the most from the estimate
- These formulas assume average muscle. Strength athletes have more lean mass than any height-and-weight formula can predict.
- Use the same formula over time. Changes are more meaningful than the absolute number.
- Pair it with a body fat measurement. Tape-based estimates from the body fat calculator use your waist, so they respond to real changes in fat.
- Drug dosing is a clinical decision. Some medicines are dosed on lean or ideal body weight, but only your prescriber or pharmacist should make that calculation.
Related tools: the body surface area calculator and the ideal weight calculator. This is not medical advice; talk to a doctor or registered dietitian.
Sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol 1984;247(4 Pt 2):F632–636.
- James WPT. Research on obesity: a report of the DHSS/MRC group. London: HMSO, 1976.
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19(4):389–391.
- Peters AM, Snelling HL, Glass DM, Bird NJ. Estimation of lean body mass in children. Br J Anaesth 2011;106(5):719–723.
- Bird NJ, Henderson BL, Lui D, Ballinger JR, Peters AM. Indexing glomerular filtration rate to suit children. J Nucl Med 2003;44(7):1037–1043.
Frequently asked questions
What is lean body mass?
Lean body mass is everything in your body that is not fat: muscle, bone, organs, skin and water. It is your weight minus your fat mass. Doctors and pharmacists use estimates of it to dose some medicines, and it is a useful way to see whether weight change is mostly fat or mostly muscle.
How do I calculate my lean body mass?
With the Boer formula, men use 0.407 × weight (kg) + 0.267 × height (cm) − 19.2 and women 0.252 × weight + 0.473 × height − 48.3. A man 5 ft 10 in tall weighing 180 lb gets about 135.6 lb of lean mass, which implies about 24.7% body fat.
Which lean body mass formula is most accurate?
None is best for everyone. Boer is common in clinical work, James is used in some anaesthesia dosing but becomes unreliable at high BMI, and Hume tends to give the lowest values. Because all three use only height and weight, a tape-based or lab body-fat measurement will be closer for most people.
Can I use this lean body mass calculator for a child?
Yes, for children under 14 it uses the Peters formula, 3.8 × 0.02154 × weight^0.6469 × height^0.7236. A child weighing 30 kg at 138 cm gets about 26.1 kg of lean mass. The adult formulas are not designed for children.
Why does the James formula give strange results for some people?
The James formula subtracts a term based on weight divided by height, squared. Past a BMI of about 43 for men and 36 for women, that term grows faster than weight, so the estimate starts to fall as weight rises. The calculator warns you when you are in that range.