Lean Body Mass Calculator
Enter your sex, weight and height to estimate your lean body mass, fat mass and body fat percentage with three established formulas side by side.
All formulas compared
| Formula | Lean body mass | Fat mass | Body fat % |
|---|
Estimates only, for information – not medical advice. These formulas were developed for average adults and can be off for very muscular, very lean, elderly or obese people. DEXA, bioimpedance or skinfold tests measure body composition directly.
How to use the Lean Body Mass Calculator
- Choose metric or imperial units.
- Select your sex and enter your weight and height.
- Pick a main formula – Boer, James, Hume – or enter a body fat percentage you already know.
- Press Calculate LBM to see lean mass, fat mass and body fat %.
- Compare formulas in the table below; the average is a reasonable middle estimate.
Lean body mass formulas
Lean body mass (LBM) is everything except fat: muscle, bone, organs, skin and water. W is weight in kilograms and H is height in centimeters.
| 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 |
Fat mass = weight − LBM, and body fat % = fat mass ÷ weight × 100. If you already know your body fat percentage from a scan or caliper test, LBM = weight × (1 − body fat %).
Worked example
A man weighing 80 kg and 180 cm tall: Boer gives 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.42 kg of lean mass, so fat mass is 18.58 kg and body fat is about 23.2%. James gives 1.1 × 80 − 128 × (80/180)² = 88 − 25.28 = 62.72 kg, and Hume gives 0.32810 × 80 + 0.33929 × 180 − 29.5336 = 57.79 kg.
Body fat ranges (American Council on Exercise)
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25% + | 32% + |
Why lean body mass matters
- Medication dosing: some drugs, such as anesthetics and certain antibiotics, are dosed by lean rather than total weight. The Boer and James formulas are widely used in pharmacology.
- Nutrition: protein targets (for example 1.6–2.2 g per kg of lean mass for strength training) and the Katch–McArdle BMR formula use LBM.
- Progress tracking: during weight loss, keeping LBM steady while fat mass drops is the goal.
Frequently asked questions
What is lean body mass?
Lean body mass is your total weight minus your fat mass. It includes muscles, bones, organs, skin, blood and water. For most adults it is 60–90% of body weight.
Which lean body mass formula is the most accurate?
Studies suggest the Boer formula is the most accurate for most adults of normal weight. The James formula can give odd results for people with obesity, which is why the tool shows all three.
Is lean body mass the same as muscle mass?
No. Muscle is only part of lean mass – roughly half. Lean mass also includes bones, organs and body water.
How can I increase my lean body mass?
Resistance training, eating enough protein (around 1.6 g per kg of body weight per day for active people) and getting enough sleep help build lean mass over time.
How accurate are these estimates?
They are population formulas based on height and weight only, so individual results can be off by several kilograms, especially for athletes or people with obesity. DEXA scans measure body composition much more precisely.
Is this medical advice?
No. These are estimates for general information. Ask a healthcare professional for medical decisions such as drug dosing.