How this calculator works
Lean body mass is your body weight minus fat mass: muscle, bone, organs, connective tissue and body water. It is a more useful number than total weight for tracking training progress, comparing body composition between people of different heights, or estimating medication doses that scale with metabolically active tissue rather than fat.
Because LBM cannot be measured directly without tools like DEXA scans or bioelectrical impedance, several formulas have been published that estimate it from just height, weight and sex. This calculator shows the three most commonly cited — Boer, James and Hume — side by side, since they can disagree by a few kilograms for the same person. If you already know your body fat percentage from a scan or skinfold test, switch to that mode for a simpler, more direct estimate: LBM = weight × (1 − body fat % ÷ 100). These are general estimates for fitness tracking, not medical advice or a substitute for clinical body-composition testing.
The formulas (weight in kg, height in cm)
Boer (1984) — men: LBM = 0.407W + 0.267H − 19.2Boer (1984) — women: LBM = 0.252W + 0.473H − 48.3James (1976) — men: LBM = 1.1W − 128×(W/H)²James (1976) — women: LBM = 1.07W − 148×(W/H)²Hume (1966) — men: LBM = 0.32810W + 0.33929H − 29.5336Hume (1966) — women: LBM = 0.29569W + 0.41813H − 43.2933From body fat %: LBM = weight × (1 − body fat % ÷ 100)Boer is the formula most widely used in general clinical practice today. James is used in some drug-dosing contexts but is known to behave less predictably at higher body weights. Hume is older and still appears in anesthesia dosing literature.
Worked example: man, 80 kg, 180 cm
- Boer: 0.407×80 + 0.267×180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.42 kg.
- James: 1.1×80 − 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.
- The three estimates span about 57.8-62.7 kg — a normal amount of disagreement between formulas, all within a few percent of each other.
Frequently asked questions
Which lean body mass formula is most accurate?
None of them is exact — they are all regression equations fit to specific study populations decades ago, and none replaces a direct measurement like a DEXA scan. Boer is the most commonly used general-purpose formula today; the body-fat-percentage method is more direct if you already have a reliable body fat measurement.
Why do the three formulas give different answers?
Each was derived from a different research sample using slightly different statistical methods. The James formula in particular uses a squared weight-to-height term that can diverge noticeably from the linear Boer and Hume formulas at higher body weights.
Is lean body mass the same as muscle mass?
No. Lean body mass includes muscle plus bone, organs, connective tissue and body water — muscle is only part of it. Changes in hydration alone can shift LBM estimates without any real change in muscle.
How is lean body mass used in medicine?
It is used to estimate resting metabolic rate, to index some drug doses (particularly in obese patients, where dosing by total body weight can overshoot), and in body composition and nutrition research. This calculator is for general reference; clinical dosing decisions are made by a qualified professional.
Can I estimate lean body mass without already knowing my body fat percentage?
Yes. The Boer, James and Hume formulas only need your height, weight and sex — none of them require a body fat percentage. The body-fat-percentage method (LBM = weight × (1 − body fat % ÷ 100)) is a separate, more direct option for when you already have a reliable body fat measurement from a scan or skinfold test, but it isn't required to get an estimate.