Lean Body Mass Calculator: Know Your True Muscle Mass
Why Lean Mass Matters More Than Weight
Lean Body Mass = Total Weight – Fat Mass. It includes muscle, bone, organs, and water. Two people at 75 kg can look completely different — one at 18% body fat (61.5 kg lean mass) vs one at 30% (52.5 kg lean mass).
Estimation Formulas
| Formula | Best For | Inputs Needed |
|---|---|---|
| Boer (1984) | General population | Height, weight, gender |
| James (1976) | Normal BMI range | Height, weight, gender |
| Hume (1966) | Clinical settings | Height, weight, gender |
| Body fat method | Most accurate (if BF% known) | Weight, body fat % |
Lean Mass Benchmarks
| Category | Men (% of weight) | Women (% of weight) |
|---|---|---|
| Athletic | 80–88% | 75–82% |
| Healthy | 75–80% | 70–75% |
| Average | 70–75% | 65–70% |
| Below average | < 70% | < 65% |
Why Track Lean Mass?
- During weight loss: ensure you’re losing fat, not muscle
- For body recomposition: gain muscle while losing fat
- Calorie needs: lean mass drives your BMR
- Drug dosing: many medications are dosed per kg of lean mass, not total weight
Calculate your lean body mass with the lean body mass calculator.