calculators.dev

Lean Body Mass Calculator

Lean body mass (LBM) is everything in your body that is not fat: muscle, bone, organs, and water. This calculator estimates it from your sex, weight, and height using three classic formulas — Boer, James, and Hume — which are widely used in clinical settings and for drug dosing. Boer is highlighted as the most commonly cited, and the other two are shown so you can see the natural spread. These are estimates from population equations, not direct measurements, so they can differ from a body-composition scan. They are most useful for tracking change over time and as an input to more accurate metabolic formulas like Katch-McArdle.

Calculate

Default result: 135.3 lb

Each formula uses different constants for men and women.

Lean Body Mass Calculator · Result

calculators.dev

Boer (most cited)

135.3 lb

male × 176 lb × 70.9 in

James (1976)
138.1 lb
Hume (1966)
127.3 lb
135.3 lb

This calculator provides an estimate for general information only and is not a medical diagnosis or professional advice. Body-composition and health-risk figures are approximations from population formulas and can differ meaningfully from clinical measurement. Do not use this result to diagnose, treat, or rule out any health condition — consult a qualified healthcare provider before acting on it.

Reviewed by the calculators.dev team · Last updated 2026-06-23

Formula reviewed against Boer P. Estimated lean body mass as an index for normalization of body fluid volumes. Am J Physiol 1984 (Boer formula)

How to calculate

Choose your sex and enter your weight and height. Each formula combines weight and height with sex-specific constants to estimate fat-free mass. For an 80 kg, 1.80 m man, Boer returns 61.4 kg, James 62.7 kg, and Hume 57.8 kg. Boer is shown as the primary figure; the alternates appear beside it. Because the three methods disagree by a few kilograms, treat the band they form as your estimate rather than fixating on one number.

Boer (men): LBM = 0.407 × weight_kg + 0.267 × height_cm − 19.2 (women use 0.252, 0.473, −48.3). James (men): LBM = 1.1 × weight_kg − 128 × (weight_kg ÷ height_cm)². Hume (men): LBM = 0.32810 × weight_kg + 0.33929 × height_cm − 29.5336. Variables: weight in kilograms and height in centimetres (the calculator converts your units). The result is fat-free mass in kilograms. The formulas are regressions that estimate composition from size alone, so they cannot capture an individual's actual muscle-to-fat ratio.
Example calculation

For a man weighing 80 kg at 1.80 m (180 cm), the Boer formula gives 0.407 × 80 + 0.267 × 180 − 19.2 = 61.42 kg of lean mass. The James (62.7 kg) and Hume (57.8 kg) formulas are shown alongside; the roughly 5 kg spread between methods is why the result is best read as a range.

boer
61.4 kg
james
62.7 kg
hume
57.8 kg

Assumptions

  • The formulas estimate fat-free mass from weight and height only; they do not measure muscle directly and cannot account for an unusually lean or heavily muscled build.
  • Boer, James, and Hume are population regressions and disagree by a few kilograms for the same inputs, so the honest output is a range.
  • Results assume an adult of typical body composition; at the extremes of body size the estimates lose accuracy.

Common mistakes

  • Reading one formula's value as exact. The three methods differ by several kilograms — use the range they cover.
  • Confusing lean body mass with muscle mass. LBM includes bone, organs, and water, so it is always larger than skeletal muscle alone.
  • Expecting these height-and-weight formulas to match a DEXA scan precisely. They are estimates, not measurements.

Frequently asked questions

What is lean body mass?

Lean body mass is your total weight minus your fat mass — muscle, bone, organs, connective tissue, and body water. It is not the same as muscle mass, which is only part of it.

Which lean body mass formula should I use?

Boer is the most widely cited and is highlighted here, but James and Hume are also valid. Because they disagree by a few kilograms, the range across all three is more informative than any single value.

Is lean body mass the same as muscle mass?

No. Lean body mass includes bone, organs, and water as well as muscle, so it is always higher than muscle mass alone. To estimate fat mass, subtract lean body mass from total weight.

How accurate are these estimates?

They are reasonable approximations for typical adults but can differ from a DEXA or hydrostatic measurement by several kilograms, especially for very lean or very muscular people. Use them to track trends, not as exact figures.

Next in this project