Lean Body Mass Calculator
Quick answer
Estimate your lean (fat-free) body mass with the Boer equation — a widely used clinical formula built from height and weight. Add your body fat % if you already have it from the Body Fat Calculator for a more precise number, and see your fat mass and body-fat share alongside.
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The Boer equation
Men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
Women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3
With a known body fat %: LBM = weight × (1 − body fat % ÷ 100)
Published by Peter de Boer in 1984 and still used today to scale body-fluid volumes and clinical dosing. If you enter a body fat %, we use the direct method instead — it is usually more accurate than any weight-based estimate.
Worked example
- 1
A woman, 165 cm tall and 68 kg.
- 2
LBM = 0.252 × 68 + 0.473 × 165 − 48.3 = 17.1 + 78.0 − 48.3 ≈ 46.8 kg.
- 3
Fat mass = 68 − 46.8 ≈ 21.2 kg, so this estimate implies about 31% body fat.
- 4
If her measured body fat is 28% instead: LBM = 68 × 0.72 = 48.96 kg.
Interpreting your lean body mass
| Your result | Category | What it means |
|---|---|---|
| A large share of your weight | Higher lean mass | More metabolically active tissue — a higher resting calorie burn and better support for strength, training and recovery. |
| A small share of your weight | Lower lean mass | Less muscle relative to fat, usually with a lower BMR. Resistance training and adequate protein help raise it over time. |
| Fat mass | The rest of your weight | Total weight minus lean body mass. Fat is not inherently good or bad — its proportion relative to lean mass is what matters for metabolic health. |
| Same weight, different shape | Why frame matters | Two people at an identical scale weight can look very different — lean mass and frame size explain the difference. |
Lean body mass is everything that is not fat: muscle, bone, organs and body water. It is the biggest single driver of your BMR.
Frequently asked questions
Sources & further reading
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Open the logThis calculator provides general estimates for informational purposes only and is not medical advice. For personal guidance, consult a qualified healthcare provider.