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Free Lean Body Mass Calculator

Estimate your lean body mass (LBM) and body-fat mass from your sex, weight, and height using the validated Boer formula. Results update live in kilograms or pounds, with no sign-up and nothing sent to a server.

Lean body mass
61.4 kg
Body-fat mass
18.6 kg
Estimated body fat
23.2%

Estimated with the Boer (1984) formula. Lean body mass includes muscle, bone, organs, and water; the remainder is body-fat mass. These are population estimates, not a clinical body-composition measurement.

Estimate only. This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

Quick answer

Lean body mass is your total body weight minus body-fat mass — it includes muscle, bone, organs, and water. This calculator uses the Boer formula: 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. Body-fat mass is simply your weight minus that LBM figure.

Formula & method

The calculator applies the Boer (1984) formula, which estimates lean body mass from weight and height with separate equations for each sex. 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. The result is in kilograms. Imperial inputs are converted first (1 lb = 0.45359237 kg, 1 in = 2.54 cm) before the formula is applied. Body-fat mass is then computed as total weight minus LBM, and estimated body-fat percentage as body-fat mass divided by total weight, times 100. All math runs in your browser as you type; nothing is uploaded.

Examples

Example 1: Male, 80 kg, 180 cm
Input
Sex: male, weight 80 kg, height 180 cm
Result
LBM = 61.42 kg; body-fat mass = 18.58 kg (about 23.2%)
Why
0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.42 kg. Body-fat mass = 80 − 61.42 = 18.58 kg.
Example 2: Female, 65 kg, 168 cm
Input
Sex: female, weight 65 kg, height 168 cm
Result
LBM = 47.54 kg; body-fat mass = 17.46 kg (about 26.9%)
Why
0.252 × 65 + 0.473 × 168 − 48.3 = 16.38 + 79.464 − 48.3 = 47.54 kg. Body-fat mass = 65 − 47.54 = 17.46 kg.
Example 3: Male, 90 kg, 175 cm
Input
Sex: male, weight 90 kg, height 175 cm
Result
LBM = 64.15 kg; body-fat mass = 25.85 kg (about 28.7%)
Why
0.407 × 90 + 0.267 × 175 − 19.2 = 36.63 + 46.725 − 19.2 = 64.155 ≈ 64.15 kg. Body-fat mass = 90 − 64.15 = 25.85 kg.
Example 4: Female, 55 kg, 160 cm
Input
Sex: female, weight 55 kg, height 160 cm
Result
LBM = 41.24 kg; body-fat mass = 13.76 kg (about 25.0%)
Why
0.252 × 55 + 0.473 × 160 − 48.3 = 13.86 + 75.68 − 48.3 = 41.24 kg. Body-fat mass = 55 − 41.24 = 13.76 kg.

When to use this tool

  • Setting a realistic protein or calorie target, since many nutrition guidelines are expressed per kilogram of lean mass rather than total body weight.
  • Tracking body-recomposition progress over time — comparing LBM and body-fat-mass estimates between weigh-ins can show whether weight change is muscle or fat, more usefully than scale weight alone.
  • Estimating medication or anesthesia dosing context, or athletic baselines, where clinicians and coaches sometimes scale to lean mass instead of total weight.
  • Getting a quick body-composition snapshot when you don't have access to a DEXA scan, bioelectrical impedance scale, or skinfold calipers.

Common mistakes

  • Mixing up the male and female equations. The two Boer formulas use very different coefficients and constants, so always select the correct sex first — the same body would otherwise get a meaningfully wrong result.
  • Entering height in metres or inches when the formula expects centimetres. If you type 1.8 instead of 180 cm, the LBM collapses to a nonsensical value. Use the imperial mode to let the tool convert feet and inches for you.
  • Treating the estimate as a measured value. Boer-formula LBM is a population estimate from height and weight only; it does not 'see' your actual muscle or fat. A lean athlete and a sedentary person of identical height and weight get the same number.
  • Confusing lean body mass with fat-free mass or with muscle mass. LBM by some conventions includes a small amount of essential fat, and it is much more than just muscle — it also counts bone, organs, blood, and water.

Frequently asked questions

What is lean body mass?

Lean body mass (LBM) is everything in your body that is not stored fat — muscle, bone, organs, connective tissue, and the water inside them. It is your total body weight minus body-fat mass. By the most common convention LBM still includes a small amount of essential fat, which is why it differs slightly from 'fat-free mass.'

Which formula does this calculator use?

It uses the Boer (1984) formula, one of the most widely cited LBM equations. Males: LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2. Females: LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. Boer is popular in clinical and pharmacology settings because it tends to track measured lean mass well across a normal weight range.

How accurate is a formula-based LBM estimate?

It is a reasonable estimate for people of typical build, but it relies only on height, weight, and sex. It cannot account for how muscular or how lean you actually are, so a bodybuilder and a sedentary person with the same height and weight receive the same number. For precise body composition, use DEXA, hydrostatic weighing, air-displacement (Bod Pod), or validated bioimpedance.

What is the difference between lean body mass and fat-free mass?

Fat-free mass (FFM) excludes all body fat, including essential fat. Lean body mass typically includes a small percentage of essential fat needed for normal physiology. In practice the two terms are often used loosely as synonyms, but FFM is the strictly fat-free portion while LBM is slightly larger.

Is lean body mass the same as muscle mass?

No. Muscle is only one component of lean body mass. LBM also includes your skeleton, organs, skin, blood, and body water, which together make up far more than skeletal muscle. Skeletal muscle is usually only around 40–50% of lean body mass.

Can I use pounds and feet instead of kilograms and centimetres?

Yes. Switch to imperial mode and the calculator converts your pounds and feet/inches to kilograms and centimetres (1 lb = 0.45359237 kg, 1 in = 2.54 cm) before applying the Boer formula, then shows the result back in pounds.

Does the calculator send my data anywhere?

No. All calculations run locally in your browser using JavaScript. Your weight, height, and sex are never uploaded or stored on a server.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

Disclaimer

This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

  • ✓ Free to use
  • ✓ No sign-up required
  • ✓ Runs entirely in your browser — nothing is uploaded.
  • ✓ Formula and method shown above
Last updated: How we calculateReport a correctionDisclaimer

Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.

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