Lean Body Mass Calculator
Estimate lean body mass using three established anthropometric formulas — Boer, James, and Hume. Enter height, weight, and sex to see each formula's estimate in kg and as a percentage of body weight.
How It's Calculated
Formula
\text{Boer (male)} = 0.407w + 0.267h - 19.2
\text{Boer (female)} = 0.252w + 0.473h - 48.3
\text{James (male)} = 1.10w - 128(w/h)^2
\text{James (female)} = 1.07w - 148(w/h)^2
\text{Hume (male)} = 0.3281w + 0.33929h - 29.5336
\text{Hume (female)} = 0.29569w + 0.41813h - 43.2933This calculator estimates lean body mass (LBM) — the portion of body weight that isn't fat mass, including muscle, bone, organs, and water — using three established anthropometric equations: Boer (1984), James (1976), and Hume (1966). Each formula takes only weight (kg) and height (cm), with separate constants for male and female, and estimates lean mass without requiring circumference measurements or a body-fat scan. Because these are population-derived formulas rather than direct measurements (like DEXA scanning), the three estimates typically differ by a few kilograms for the same person — showing all three, alongside each one's share of total body weight, gives a more honest picture than presenting a single number as exact. This is an estimate for general informational and educational purposes, based on a published formula — it is not a medical diagnosis, and it is not a substitute for individualized advice from a qualified healthcare provider. For an input where a formula's result would be physically impossible (zero, negative, or greater than total body weight), this calculator does not silently force a number into range — it reports that the input falls outside that formula's valid domain instead.
Worked Examples
Male, 180 cm, 80 kg
- Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.42 kg
- James: 1.10 × 80 − 128 × (80/180)² = 88 − 25.28 ≈ 62.72 kg
- Hume: 0.3281 × 80 + 0.33929 × 180 − 29.5336 = 26.25 + 61.07 − 29.53 ≈ 57.79 kg
Female, 165 cm, 60 kg
- Boer: 0.252 × 60 + 0.473 × 165 − 48.3 = 15.12 + 78.05 − 48.3 = 44.87 kg
- James: 1.07 × 60 − 148 × (60/165)² = 64.2 − 19.57 ≈ 44.63 kg
- Hume: 0.29569 × 60 + 0.41813 × 165 − 43.2933 = 17.74 + 68.99 − 43.29 ≈ 43.44 kg
Frequently Asked Questions
Why do the three formulas give different results?
Boer, James, and Hume were each derived from different reference populations and use different weight/height coefficients. None of them measures your actual body composition directly — they're all estimates from a formula, so some disagreement between them is expected. Comparing all three is more informative than trusting one in isolation.
What does the percentage figure mean?
It's that formula's lean body mass estimate divided by your total entered body weight, shown as a percentage — for example, a Boer estimate of 61.42 kg on an 80 kg body is 76.8% lean mass.
What happens if my inputs produce an impossible result?
If a formula's raw output would be zero, negative, or greater than your entered body weight, this calculator reports that your inputs fall outside that formula's valid range instead of showing a physically meaningless number.
Is this the same as a body-fat percentage measurement?
No. Lean body mass and body-fat percentage are two views of the same underlying split (lean mass + fat mass = total weight), but this calculator estimates lean mass directly from weight and height, while a body-fat calculator like this site's Navy-method tool estimates fat percentage from circumference measurements — they use different formulas and different inputs.