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Lean Body Mass Calculator

Estimate your lean body mass from sex, height and weight with the Boer, James and Hume formulas, or the Peters formula for children, and see the matching body fat estimate.

Units
Under 14 uses the Peters formula for children.
Height
ft
in
From a scale, caliper or scan. Gives a lean mass based on your own measurement.

Results are estimates from population formulas, not medical advice.

Read the guide What Is Lean Body Mass and How Do You Estimate It?

How to use the lean body mass calculator

  • Choose US or Metric units.
  • Select your sex and enter your height and weight.
  • Optionally enter your age. For children under 14 the calculator switches to the Peters formula, which was developed for children.
  • Optionally enter a known body fat % from a body fat scale, skinfold caliper or DEXA scan to also see lean mass based on your own measurement.
  • Press Calculate. The result shows lean body mass for each formula, as a weight and as a percentage of your total weight, together with the matching body fat estimate.

What lean body mass means

Lean body mass (LBM) is everything in your body except fat: muscle, bone, organs, skin and body water. It is used in some medication dosing, in the Katch-McArdle calorie formula and for tracking whether weight loss comes from fat or from muscle. The calculator estimates body fat as weight − lean body mass.

The formulas

All formulas use weight in kg and height in cm. US values are converted first.

  • Boer: men 0.407 × weight + 0.267 × height − 19.2; women 0.252 × weight + 0.473 × height − 48.3
  • James: men 1.1 × weight − 128 × (weight / height)²; women 1.07 × weight − 148 × (weight / height)²
  • Hume: men 0.32810 × weight + 0.33929 × height − 29.5336; women 0.29569 × weight + 0.41813 × height − 43.2933
  • Peters (children): 3.8 × 0.0215 × weight^0.6469 × height^0.7236
  • From body fat %: weight × (1 − body fat % / 100)

The headline result uses your body fat % when you enter one, otherwise the Boer formula for adults or the Peters formula for children.

Worked example

A man who is 180 cm tall and weighs 80 kg:

  • Boer: 32.56 + 48.06 − 19.2 = 61.4 kg, which is 76.8% of his weight, so about 18.6 kg (23.2%) is body fat
  • James: 88 − 128 × 0.1975 = 62.7 kg (78.4%)
  • Hume: 26.25 + 61.07 − 29.53 = 57.8 kg (72.2%)
  • If a scan shows 20% body fat: 80 × 0.80 = 64 kg of lean mass

Good to know

  • These formulas were built from average adults. Very muscular or very heavy people can get results that are far off. The James formula stops working at a very high weight for a given height; the calculator then marks it as not valid.
  • A measured body fat percentage is usually more accurate than any height and weight formula.
  • The formulas differ by a few kilograms, so treat the range as your estimate.
  • Results are estimates, not medical advice. For medication dosing, always follow your doctor or pharmacist.

Frequently asked questions

Which lean body mass formula is the most accurate?

No single formula is best for everyone. The Boer formula is often preferred for adults of normal weight, the James formula becomes unreliable at high body weight, and the Hume formula tends to give slightly lower values. If you know your body fat percentage from a reliable measurement, lean mass based on it is usually the best estimate.

What is a normal lean body mass percentage?

For many adult men lean mass is roughly 75–85% of body weight, and for many adult women roughly 65–80%. The rest is body fat. Athletes are often higher, and people with more body fat are lower.

Is lean body mass the same as muscle mass?

No. Lean body mass includes muscle but also bone, organs, skin, blood and body water. Muscle is usually a bit less than half of lean mass.

Why is there a separate formula for children?

Children have different body proportions and composition from adults, so adult formulas can be misleading for them. The Peters formula was developed from data on children and is used here when the age entered is under 14.