Lean Body Mass Calculator
Estimate lean body mass with the Boer, James and Hume equations from sex, height and weight — with estimated fat mass and body fat percent.
About the Lean Body Mass Calculator
Lean body mass (LBM) is everything in your body except fat: muscle, bone, organs and water. This calculator estimates it from just your sex, height and weight using the three standard prediction equations — Boer, James and Hume — and derives your estimated fat mass and body fat percentage from the Boer result.
The Boer formula (for men: 0.407×weight + 0.267×height − 19.2; for women: 0.252×weight + 0.473×height − 48.3, with weight in kg and height in cm) is the most widely used, including clinically for scaling drug doses. James and Hume are shown alongside so you can see the plausible range — the three usually agree within a couple of kilograms for typical builds.
LBM matters for setting protein targets, judging whether weight change is fat or muscle, and normalising strength standards. Remember these are population-level formulas: a DEXA scan or other body-composition measurement will beat any equation for individual accuracy.
How to Use the Lean Body Mass Calculator
- 1Select your sex.
- 2Enter your height in centimetres and weight in kilograms.
- 3Read your lean body mass from the Boer, James and Hume formulas.
- 4Use the derived fat mass and body fat percentage as a rough composition check.
Frequently Asked Questions
How is lean body mass calculated? A worked example
For a 78 kg, 175 cm man, the Boer formula gives LBM = 0.407 × 78 + 0.267 × 175 − 19.2 = 31.7 + 46.7 − 19.2 ≈ 59.3 kg. Fat mass is then 78 − 59.3 = 18.7 kg, about 24% body fat.
Which formula is most accurate — Boer, James or Hume?
Boer is the usual default and validates best against scans across the widest range of body types; it's also the formula used clinically for lean-mass-scaled drug dosing. James tends to underestimate LBM in people with obesity (its quadratic term misbehaves at high weights). When the three disagree noticeably, trust Boer or get a scan.
What is a normal lean body mass percentage?
LBM as a share of total weight typically runs about 75–90% for men and 70–85% for women — the mirror image of normal body-fat ranges (men ~10–25%, women ~15–30%). Athletes sit at the top of the range, since more muscle and less fat both push LBM percentage up.
Why do women have lower LBM formulas than men?
Women physiologically carry more essential fat (roughly 10–13% of body weight versus 2–5% for men) and on average less muscle mass, so the female coefficients weight height and body mass differently. Comparing your LBM against same-sex norms is the meaningful comparison.
How does lean body mass help with protein and calorie targets?
Recommendations scale better with LBM than total weight, especially at higher body fat. A common strength-training protein target is 1.6–2.2 g per kg of LBM — for the 59.3 kg LBM example above, roughly 95–130 g of protein per day. BMR estimates based on LBM (like Katch-McArdle) are also more accurate for muscular or lean individuals.