What is lean body mass?

Lean body mass (LBM) is the total weight of your body minus your body fat. It includes muscle, bone, organs, skin, and water. Tracking LBM alongside total weight gives a clearer picture of body composition changes during diet or training.

What is the Boer formula?

The Boer (1984) formula estimates lean body mass from weight and height. For men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2. For women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3. It was published by P. Boer in the American Journal of Physiology, volume 247 (1984).

How is lean body mass different from total weight?

Total weight includes both lean mass and fat mass. Lean body mass is the portion that is not fat, covering muscle, bone, organs, and water. Two people with the same total weight can have very different body compositions.

Is my data sent to a server?

All calculations run locally in your browser using JavaScript. No data is sent to our servers at any point.

Lean body mass calculator

Lean body mass calculator is a health tool that estimates lean mass, fat mass, and implied body fat percentage using the Boer (1984) formula. It supports metric and imperial units, switches the formula by sex, and updates results as you type. The tool runs in your browser.

Sex

Units

Weight (kg)

Height (cm)

Dedicated pages

Sex-specific and alternative lean mass calculators.

Lean body mass calculator for men

Calculate lean body mass, fat mass, and body fat percentage for men using the Boer formula. Free, runs entirely in your browser.

Lean body mass calculator for women

Calculate lean body mass, fat mass, and body fat percentage for women using the Boer formula. Free, runs entirely in your browser.

Fat-free mass calculator

Calculate your fat-free mass (lean body mass) in kg and lbs using the Boer formula. Includes fat mass and implied body fat percentage. Free, in-browser.

How to calculate lean body mass

Choose your sex (male or female).
Select metric (kg, cm) or imperial (lbs, ft/in) units.
Enter your weight and height.
Your lean body mass, fat mass, and body fat percentage appear instantly.

Common uses

Assessing body composition beyond total weight during a fitness or nutrition programme
Tracking muscle gain and fat loss simultaneously alongside a BMI calculator or body fat calculator
Comparing lean mass estimates over time to monitor the effect of diet or training changes

Technical specification

Algorithm or formula: Boer (1984) formula. Men: LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2. Women: LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. Published in the American Journal of Physiology, volume 247 (1984).
Browser API or library: Pure JavaScript arithmetic. No external library.
Input limits: Numeric weight and height. Imperial values convert to metric internally.
Output: Lean body mass (kg or lbs), fat mass, and implied body fat percentage = (total − LBM) / total.
Known limitations: A prediction formula, not a measurement. Margin of error is generally a few percent versus DEXA, with poorer accuracy at extreme body compositions.

Frequently asked questions

What is lean body mass?: Lean body mass (LBM) is the total weight of your body minus your body fat. It includes muscle, bone, organs, skin, and water. Tracking LBM alongside total weight gives a clearer picture of body composition changes during diet or training.
What is the Boer formula?: The Boer (1984) formula estimates lean body mass from weight and height. For men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2. For women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3. It was published by P. Boer in the American Journal of Physiology, volume 247 (1984).
How is lean body mass different from total weight?: Total weight includes both lean mass and fat mass. Lean body mass is the portion that is not fat, covering muscle, bone, organs, and water. Two people with the same total weight can have very different body compositions.
Is my data sent to a server?: All calculations run locally in your browser using JavaScript. No data is sent to our servers at any point.

Reviewed and tested May 26, 2026.