Lean Body Mass Calculator
Estimate your lean body mass (LBM), the part of your weight that is not fat, with this free calculator. It compares the Boer, James and Hume formulas and shows your fat mass. If you know your body fat percentage, add it for a more personal result.
What is lean body mass?
Lean body mass (LBM) is your total body weight minus the weight of your body fat. It includes your muscles, bones, organs, skin, blood and water. For most adults, lean mass makes up about 60–90% of body weight. Because lean tissue, especially muscle, burns more energy than fat, a higher lean body mass usually means a faster metabolism and better strength, balance and long-term health.
Doctors also use lean body mass to work out doses of some medicines, such as anaesthetics, because many drugs are distributed mainly through lean tissue rather than fat.
Lean body mass formulas
This calculator uses three well-known formulas, with weight in kg and height in cm:
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407W + 0.267H − 19.2 | 0.252W + 0.473H − 48.3 |
| James (1976) | 1.1W − 128 × (W/H)² | 1.07W − 148 × (W/H)² |
| Hume (1966) | 0.32810W + 0.33929H − 29.5336 | 0.29569W + 0.41813H − 43.2933 |
Example: A man who weighs 80 kg and is 180 cm tall has a lean body mass of about 61.4 kg using the Boer formula, 62.7 kg using James and 57.8 kg using Hume. With the Boer result, his estimated fat mass is about 18.6 kg.
Lean body mass from body fat percentage
If you already know your body fat percentage, from a scan, smart scale or our Body Fat Calculator, you can work out your lean mass more personally:
LBM = weight × (1 − body fat % ÷ 100)
For example, someone who weighs 80 kg with 20% body fat has 80 × 0.8 = 64 kg of lean mass and 16 kg of fat mass. This is usually more accurate than the height-and-weight formulas, because it reflects your actual body composition.
Which formula is most accurate?
The Boer formula is generally considered the most reliable for most adults and is widely used. The James formula works well for people of normal weight but becomes inaccurate at high body weights, where it can even give very low results. The Hume formula is one of the oldest and tends to give slightly lower values. None of the formulas can tell a muscular person from a less active person of the same size, so a body fat measurement always gives a more personal answer.
What is a healthy lean body mass?
There is no single target, because lean mass depends on your height, frame and sex. A more useful way to judge it is through body fat percentage. For men, a healthy body fat of about 8–24% means roughly 76–92% lean mass. For women, a healthy body fat of about 21–35% means roughly 65–79% lean mass. Men usually have more lean mass than women of the same weight.
How to increase lean body mass
Building lean mass takes three things: regular strength training with gradually heavier loads, enough protein (often 1.6–2.2 g per kg of body weight for people who lift), and good recovery with enough sleep. Eating a small calorie surplus helps muscle growth, while eating in a small deficit with high protein and strength training can help you lose fat while keeping your muscle. Use our Calorie Calculator and Macro Calculator to plan your intake.
Frequently Asked Questions
What is the difference between lean body mass and fat-free mass?
They are very similar and often used to mean the same thing. Strictly speaking, lean body mass includes a small amount of essential fat inside organs and bone marrow, while fat-free mass excludes all fat. The difference is only a few percent.
How do I calculate my lean body mass?
The simplest way is to use a formula such as Boer, which only needs your height, weight and sex. If you know your body fat percentage, multiply your weight by (1 − body fat % ÷ 100) for a more personal result.
Is lean body mass the same as muscle mass?
No. Muscle makes up about half of lean body mass. The rest is bones, organs, skin, blood and water.
Can I lose fat without losing lean mass?
Yes, mostly. Eating enough protein, doing strength training and losing weight slowly (about 0.5 kg a week) helps you keep most of your lean mass while losing fat.
Why does lean body mass matter?
More lean mass supports a healthy metabolism, strength, balance and blood sugar control, and helps protect against frailty as you age. It is also used by doctors to calculate some medicine doses.