Lean Body Mass Calculator (Boer Formula)
Estimate lean body mass and fat mass from height, weight and sex using the Boer equation, with the accuracy limits of a predictive formula.
Results
- Lean body mass
- 58.1 kg
- Boer equation estimate
- Fat mass
- 17 kg
- Bodyweight minus lean mass
- Estimated body fat
- 22.6%
- Derived from the lean-mass estimate
- FFMI
- 19 (normalized 19.3)
- Lean mass / height2, adjusted to 1.8 m
Estimation methods compared
| Method | What it uses | Typical error |
|---|---|---|
| Boer (1984) | Sex, bodyweight, height | Several kg for individuals |
| Body-fat % method | Bodyweight + measured body fat | Depends on the body-fat method |
| DEXA / hydrostatic | Direct measurement | Reference standard |
How it works & limitations
The Boer equations
Men: LBM = 0.407 x weight(kg) + 0.267 x height(cm) - 19.2 Women: LBM = 0.252 x weight(kg) + 0.473 x height(cm) - 48.3 Lean body mass includes muscle, bone, water and organs; it is not the same as 'muscle mass'.
Accuracy
Boer is a predictive formula and can be several kilograms off for individuals, especially at extreme heights, ages or body compositions. Hydration also changes bodyweight without changing fat. If you have a body-fat measurement, the body-fat method is more direct; use the same method and conditions when tracking.
Sources
Last updated 2026-08-13
Estimate only. DEXA or hydrostatic weighing is far more accurate when body-composition decisions matter.
Frequently asked questions
What is lean body mass?
Lean body mass is bodyweight minus fat mass: muscle, bone, water and organs. It is a useful reference for tracking whether weight changes are muscle or fat, though the Boer formula is an estimate, not a DEXA scan.
How accurate is the Boer formula?
The Boer equation was developed for normalizing body fluid volumes and predicts lean mass reasonably well in healthy adults, but individual error is several kilograms. Track trends with the same formula rather than absolute numbers.