UnitConv

Lean Body Mass (LBM) Calculator

Estimate your fat-free mass with three validated formulas

Your Lean Body Mass
56.0
kg
Representative value (Boer)
Boer
56.0
kg
James
56.5
kg
Hume
52.8
kg
Lean mass
56.0 kg
Fat mass
14.0 kg

Body fat: 20.0%

Average of all formulas: 55.1 kg

Compare Formulas

Boer56.0 kg
James56.5 kg
Hume52.8 kg

Formulas Used

Boer (male): LBM = 0.407 x kg + 0.267 x cm - 19.2

James (male): LBM = 1.1 x kg - 128 x (kg / cm)^2

Hume (male): LBM = 0.32810 x kg + 0.33929 x cm - 29.5336

All formulas estimate lean (fat-free) body mass in kilograms from height, weight and sex. Boer is the representative value; fat mass is your weight minus lean mass.

What is a Lean Body Mass Calculator?

A lean body mass (LBM) calculator estimates the weight of everything in your body except fat - muscle, bone, organs, water and connective tissue. It uses your height, weight and sex with three validated equations: Boer (the representative value), James and Hume. From your LBM the tool also derives your fat mass and body-fat percentage, giving you a clear split of your body composition. LBM is useful for setting protein targets, dosing certain medications and tracking whether weight changes are muscle or fat. Both metric (cm/kg) and imperial (ft-in/lb) units are supported.

How to Use

1. Choose metric (cm/kg) or imperial (ft-in/lb) units. 2. Select your sex, then enter your height and weight. 3. Read your lean body mass - the large number is the Boer result, with James and Hume shown for comparison. 4. Check the body-composition split for your estimated fat mass and body-fat percentage.

Formula & Definition

Boer (representative): Men: LBM = 0.407 x kg + 0.267 x cm - 19.2 Women: LBM = 0.252 x kg + 0.473 x cm - 48.3 James: Men: LBM = 1.1 x kg - 128 x (kg / cm)^2 Women: LBM = 1.07 x kg - 148 x (kg / cm)^2 Hume: Men: LBM = 0.32810 x kg + 0.33929 x cm - 29.5336 Women: LBM = 0.29569 x kg + 0.41813 x cm - 43.2933 Fat mass = total weight - LBM. For example, a 175 cm, 70 kg man has a Boer LBM of about 57 kg.

Interpreting Results

Lean body mass typically makes up about 70-90% of body weight, depending on body-fat level. The three formulas usually agree within a few percent for people of average build; they become less accurate at the extremes of body size and very high body fat. Fat mass is simply your weight minus LBM, and the body-fat percentage shown follows from that. Use LBM as a baseline for nutrition planning (for example, 1.6-2.2 g of protein per kg of LBM for active people) and to judge whether you are gaining muscle or fat over time, rather than as a precise clinical measurement.

Frequently Asked Questions

What is lean body mass? ▾

Lean body mass is your total body weight minus fat mass - that is, muscle, bone, organs, water and other fat-free tissue. It is sometimes called fat-free mass.

Which LBM formula should I use? ▾

Boer is the representative value here and works well for most adults; James and Hume are shown alongside for comparison. They usually agree to within a few percent for people of average build.

How is lean body mass different from body fat? ▾

Lean body mass is everything except fat, while fat mass is the fat itself. Your body weight is the sum of the two, and body-fat percentage is fat mass divided by total weight.

Why does sex matter for LBM? ▾

On average men carry more muscle and bone and less essential fat than women, so each formula uses different coefficients for men and women to reflect those differences.

Is this the same as a body-fat test? ▾

No. These equations estimate LBM from height, weight and sex, while methods like DEXA, skinfolds or bioimpedance measure body composition more directly. Use this as a quick estimate, not a substitute for a measured test.

This tool provides a general estimate, not individual medical advice. LBM formulas are approximations and should not replace a measured body-composition assessment or guidance from a qualified healthcare professional.