Lean Body Mass Calculator
Estimate lean body mass using the Boer formula, with an optional body fat% method.
Inputs
Results
Lean body mass (LBM) is an estimate and should not replace professional medical advice.
Important Note : If body-fat % is known, the body-fat method is usually the more direct estimate; Boer is a prediction formula when body-fat % is unavailable.
Use this Lean Body Mass Calculator to estimate lean body mass (LBM) from weight, height, sex, and optional body-fat percentage. It is useful for fitness tracking, nutrition planning, and body-composition review when you want more context than body weight alone.
Reviewed by: AjaxCalculators Editorial Team
Last updated: April 23, 2026
Method source: Boer lean body mass prediction equation, plus direct lean-mass calculation from body-fat percentage
Editorial standards: AjaxCalculators Editorial Policy
What This Lean Body Mass Calculator Calculates
This calculator estimates:
- Lean body mass (Boer formula)
- Lean body mass from body-fat percentage
- Fat mass
It uses:
- Sex
- Weight
- Height
- Optional body-fat percentage
How the Lean Body Mass Calculator Works
1) Boer Formula
If body-fat percentage is not known, the page estimates lean body mass using the Boer equation.
Men:
LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
Women:
LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3
This is a prediction formula based on body size rather than a direct body-composition measurement.
2) Body-Fat Percentage Method
If body-fat percentage is known, lean body mass can be estimated more directly:
LBM = body weight × (1 − body fat % / 100)
Fat mass is then:
Fat mass = body weight × (body fat % / 100)
This route is often easier to interpret because it directly splits body weight into fat mass and non-fat mass.
Assumptions and Important Notes
- This calculator gives an estimate, not a direct body-composition measurement.
- The Boer formula is a prediction equation, so it is most useful when body-fat percentage is not available.
- If body-fat percentage is known from a reasonable measurement method, the body-fat route is the more direct estimate.
- Many sources use lean body mass (LBM) and fat-free mass (FFM) almost interchangeably in practice.
- Body-fat percentage quality matters. If the entered body-fat % is poor, the resulting lean-mass estimate will also be poor.
- For higher-accuracy assessment, methods such as DXA or validated body-composition testing are better than formula estimates.
Worked Example
Suppose someone enters:
- Sex: Male
- Weight: 80 kg
- Height: 180 cm
- Body fat: 15%
Example A: LBM from Body-Fat Percentage
Step 1: Convert body-fat percentage to decimal form
15% = 0.15
Step 2: Calculate fat mass
Fat mass = 80 × 0.15 = 12 kg
Step 3: Calculate lean body mass
LBM = 80 × (1 − 0.15) = 80 × 0.85 = 68 kg
Example B: Boer Formula
Step 1: Apply the Boer male formula
LBM = 0.407 × 80 + 0.267 × 180 − 19.2
Step 2: Calculate
LBM = 32.56 + 48.06 − 19.2 = 61.42 kg
This example shows why the two methods can give different answers: one is a direct body-fat-based split, while the other is a formula-based prediction from height and weight.
How to Use This Lean Body Mass Calculator
- Select your sex.
- Enter your weight.
- Enter your height.
- Optionally enter body-fat percentage if you know it.
- Review the Boer estimate, the body-fat-based estimate, and fat mass.
How to Interpret the Result
LBM (Boer formula) is a prediction estimate based on height and weight.
LBM (from body-fat %) is a more direct estimate when body-fat percentage is available.
Fat mass tells you the estimated portion of total body weight that is fat.
If the Boer result and body-fat-based result are meaningfully different, that does not automatically mean the calculator is wrong. It usually means the two methods are answering the same question through different assumptions.
Practical Uses of a Lean Body Mass Calculator
- estimate non-fat body mass for fitness tracking
- compare total weight with lean mass and fat mass
- understand how body-fat percentage changes lean-mass estimates
- use a quick height/weight formula when body-fat percentage is unavailable
References
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans
- Heymsfield et al. review: lean body mass and fat-free mass terminology
- AjaxCalculators live Lean Body Mass Calculator
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Disclaimer: This calculator is for educational and fitness-tracking use only. It does not replace DXA, professional body-composition testing, or clinical assessment.