Your body weight is made of two parts: fat, and everything else. That “everything else” is lean body mass, and it includes muscle, bone, organs, connective tissue and the water they contain. Lean mass matters because it is metabolically active: it largely determines how many calories you burn at rest, and it is the tissue that exercise builds and that dieting can erode. This calculator estimates it from height, weight and sex with three formulas that have been used in clinical practice for decades.
These are predictive formulas, not measurements. They are useful for planning and for comparing with other estimates, but they cannot see how much of your weight is muscle.
How to use the lean body mass calculator
- Select your sex. Each formula has separate coefficients for men and women.
- Enter your height and weight in any units.
- Read the three estimates. Boer is the most widely cited; James and Hume provide a range.
- Check the implied fat mass and body fat. Compare with the Body Fat Calculator to see whether they roughly agree.
Lean body mass formulas
W is weight in kilograms and H is height in centimetres. Results are in kilograms.
Boer (1984), women: 0.252 W + 0.473 H − 48.3
James (1976), men: 1.1 W − 128 (W ÷ H)²
James (1976), women: 1.07 W − 148 (W ÷ H)²
Hume (1966), men: 0.32810 W + 0.33929 H − 29.5336
Hume (1966), women: 0.29569 W + 0.41813 H − 43.2933
Fat mass = W − lean mass
Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol 1984;247:F632–F636. James WPT. Research on Obesity, HMSO, London 1976. Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19:389–391.
Worked example
A man who is 180 cm tall and weighs 80 kg.
- Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg
- James: 1.1 × 80 − 128 × (80 ÷ 180)² = 88 − 25.3 = 62.7 kg
- Hume: 0.3281 × 80 + 0.33929 × 180 − 29.5336 = 57.8 kg
- Fat mass from Boer = 80 − 61.4 = 18.6 kg, or 23.2% of body weight.
Typical lean mass by height and weight
Boer estimates for sample builds, with the lean share of body weight in brackets.
| Height | Weight | Lean mass, woman (Boer) | Lean mass, man (Boer) |
|---|---|---|---|
| 160 cm | 55 kg | 41.2 kg (75%) | 45.9 kg (83%) |
| 165 cm | 62 kg | 45.4 kg (73%) | 50.1 kg (81%) |
| 170 cm | 70 kg | 49.8 kg (71%) | 54.7 kg (78%) |
| 175 cm | 75 kg | 53.4 kg (71%) | 58.0 kg (77%) |
| 180 cm | 80 kg | 57.0 kg (71%) | 61.4 kg (77%) |
| 185 cm | 90 kg | 61.9 kg (69%) | 66.8 kg (74%) |
Why lean mass matters
- Energy use. Resting metabolic rate correlates strongly with lean mass; equations such as Katch-McArdle and Cunningham use it directly in the BMR Calculator.
- Protein needs. Many nutrition plans scale protein to lean or healthy weight; see the Protein Intake Calculator.
- Ageing. Lean mass declines gradually with age unless it is maintained with resistance training and enough protein.
- Dosing. The Boer formula was developed to normalise body fluid volumes and is used in some drug-dosing and imaging contexts.
Limits
All three formulas assume a typical body shape for the given height and weight. Someone with unusual muscularity will have more lean mass than predicted, and someone with a high fat percentage at the same weight will have less. Use the numbers to track trends or to compare with a body-fat estimate, such as the Navy Body Fat Calculator or the FFMI Calculator, not as proof of how much muscle you carry.
This page is for information only and is not medical or dietary advice. Speak to a doctor or registered dietitian before making large changes to your diet or exercise.
Sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol 1984;247:F632–F636.
- James WPT. Research on Obesity. Her Majesty’s Stationery Office, London, 1976.
- Hume R. Prediction of lean body mass from height and weight. J Clin Pathol 1966;19:389–391.
Frequently asked questions
What is lean body mass?
Lean body mass (LBM) is everything in your body that is not fat: muscle, bone, organs, skin and body water. It is also called fat-free mass. Resting energy use and protein needs track lean mass more closely than total weight, which is why it is useful for nutrition planning.
Which formula is best?
None is clearly superior. Boer is the most commonly quoted and was validated against measured body composition in adults. James and Hume are older formulas used in clinical dosing. They usually fall within a few kilograms of each other, so the spread is a rough measure of uncertainty.
How accurate are these estimates?
They predict lean mass from height and weight only, so they cannot tell a muscular person from a heavy person with the same measurements. Errors of several kilograms are common. A DEXA scan or bioelectrical impedance reading is more accurate.
How do I use lean mass for calories and protein?
Equations such as Katch-McArdle and Cunningham take lean mass and return resting energy; see the BMR Calculator. Protein targets are often set per kilogram of lean or healthy body weight; see the Protein Intake Calculator.
Can this tell me how much muscle I have?
No. Lean mass includes organs, bone and water along with muscle, and these formulas do not separate them. Only imaging or specialised assessments can measure skeletal muscle directly.