What is lean body mass?
Lean body mass (LBM) is everything in your body except fat: muscle, bones, organs, skin and water. It is used to dose some medicines, to estimate how many Calories you burn, and to follow whether a diet takes off fat or muscle. The calculator estimates it from your sex, height and weight with three widely used formulas.
Example: a man 5 ft 10 in tall who weighs 160 lb has a lean body mass of about 127.5 lb by the Boer formula, which puts his body fat at about 20.3%.
The formulas
- Boer (1984): men 0.407W + 0.267H − 19.2; women 0.252W + 0.473H − 48.3
- James (1976): men 1.1W − 128(W/H)²; women 1.07W − 148(W/H)²
- Hume (1966): men 0.32810W + 0.33929H − 29.5336; women 0.29569W + 0.41813H − 43.2933
W is weight in kilograms and H is height in centimeters. Boer is considered the most accurate for most adults.
How to keep lean mass
When you lose weight, part of it can be muscle. Strength training two to three times a week and enough protein, about 1.2 to 1.6 grams per kilogram of body weight a day, help you lose fat while keeping muscle.
Frequently asked questions
Is lean body mass the same as muscle mass?
No. Muscle is only part of it; lean mass also includes bones, organs and body water.
How can I measure it more precisely?
A DEXA scan or a bioelectrical impedance scale measures body composition directly. Tape measurements, as in our Body Fat Calculator, are another option.
Why do the formulas give different numbers?
Each was fitted on a different group of people. The James formula is less reliable at a high BMI.