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● Body composition

Your lean mass and fat mass.

Your weight is not all the same: part is muscle, bone and water (lean mass) and part is fat. This calculator separates the two and shows your body composition on a chart.

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Lean Mass Calculator
Lean mass and fat mass by body fat % or Boer formula — donut chart
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Your data

lb
%
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Your composition

— lean
Lean mass Fat mass
Lean mass—
Fat mass—
% lean mass—
% fat mass—
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How it's calculated

Two methods: body fat % or the Boer formula

The lean mass calculator separates your body weight into lean mass (muscle, bone, water and organs) and fat mass. You can use your known body fat percentage for a direct calculation, or let the Boer (1984) formula estimate lean mass from height and weight alone. For example, an 80 kg person at 20% body fat has 64 kg of lean mass and 16 kg of fat.

Method 1 — by body fat %: the most accurate when you have a reliable body fat measurement (DEXA scan, skinfold calipers, BIA device).

Lean mass = Weight × (1 − Body fat % ÷ 100) | Fat mass = Weight − Lean mass

Method 2 — Boer formula (1984): estimates lean mass from height and weight without needing a body fat reading. Validated across diverse populations.

Male: 0.407 × kg + 0.267 × cm − 19.2 | Female: 0.252 × kg + 0.473 × cm − 48.3
  1. 1
    Input weight and body fat % (or height for Boer method)
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  2. 2
    Apply the formula to calculate lean mass
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  3. 3
    Fat mass = Total weight − Lean mass
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Understand the terms

Lean mass (LBM)
All body weight that is not fat: muscle, bone, water, organs and connective tissue. Also called fat-free mass (FFM).
Fat mass
The total weight of fat tissue in your body, including essential fat (needed for life) and storage fat.
Boer formula
An equation published in 1984 that estimates lean body mass using height and weight, validated across diverse populations.
Body fat %
The proportion of your total body weight that is fat tissue. Measured by DEXA scan, skinfold calipers, BIA or hydrostatic weighing.
See the full glossary →
Disclaimer: estimation tool for informational and planning purposes, using reference values from 2024. The Boer formula does not account for individual muscle–bone ratios; the body-fat method depends on the accuracy of your fat measurement. Results may differ from clinical assessments. Does not replace evaluation by a doctor, dietitian or certified trainer.
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Frequently asked questions — Lean Mass

What is lean mass?
Lean mass (also called lean body mass or fat-free mass) is the portion of your body weight that is not fat. It includes muscle, bone, water, organs and connective tissue. For most people, lean mass represents 70–85% of total body weight.
What is the Boer formula for lean mass?
The Boer (1984) formula estimates lean mass from height and weight without needing a body fat measurement. For males: LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2. For females: LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3.
How do I calculate lean mass from body fat percentage?
The formula is: Lean mass = Body weight × (1 − Body fat% ÷ 100). For example, if you weigh 80 kg with 20% body fat: Lean mass = 80 × (1 − 0.20) = 64 kg. Fat mass = 80 − 64 = 16 kg.
What is a good lean mass percentage?
Typical lean mass percentages: men 75–90%, women 65–85%. Athletes generally have higher lean mass percentages. These values vary by age, sex and training history. A bodybuilder may have over 90% lean mass, while a sedentary adult may be closer to 70%.
What is the difference between lean mass and muscle mass?
Lean mass includes all non-fat tissues: muscle, bone, organs, water and connective tissue. Muscle mass refers specifically to skeletal muscle. Muscle typically accounts for about 40–50% of lean mass in adults. To isolate muscle specifically, you need a DEXA scan or MRI.

📚 Learn more — official sources

🔬 Study Boer (1984) — Lean body mass formula Original publication of the Boer formula for estimating lean body mass from height and weight. See on PubMed → 🏛️ Organization WHO — Body composition and health World Health Organization: official guidelines on body composition, obesity and overweight. See official source → 📘 Guide ISSN — Body Composition and Performance International Society of Sports Nutrition position stand on body composition assessment and lean mass. See guide → 🏛️ Organization ACE — Lean Mass and Fat Mass American Council on Exercise reference on body fat percentage ranges and lean mass for fitness assessment. See official source →

About the Lean Mass Calculator

Lean mass is one of the most meaningful numbers in body composition: it tells you how much of your weight is working tissue — muscle, bone, organs and water — versus stored fat. Tracking lean mass over time is far more useful than tracking total weight alone, especially during fat-loss or muscle-building phases.

This calculator offers two methods: a direct calculation from your known body fat percentage (the most precise when you have a reliable measurement from a DEXA scan, skinfold calipers or BIA device) and the Boer formula, which estimates lean mass from height and weight alone. All results are free, instant and require no sign-up.

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