Lean Body Mass Calculator

Estimate your lean (fat-free) body mass and fat mass from your height, weight and sex using the Boer formula.

Work out your lean body mass, the fat-free part of your weight, with this calculator based on the Boer formula. Enter your height, weight and sex to see your lean mass, your fat mass and what share of your body is lean, which is useful for tracking muscle when you diet or train.

Read the guide: Lean Body Mass: Why It Matters More Than Weight

Your measurements

Units
Sex

Lean body mass

61.4 kg

76.8% of your body weight

Fat mass
18.6 kg
Lean percent
76.8%

Lean mass

61.4 kg

  • Lean mass77%
  • Fat mass23%

Estimated with the Boer formula. A body scan is more precise. Informational only, not medical advice.

How it works

  1. 1

    Pick units and sex

    Choose metric or imperial and your sex.

  2. 2

    Enter height and weight

    Add your measurements.

  3. 3

    See the split

    View your lean mass, fat mass and lean percentage.

Instant & 100% private — nothing is uploaded

Every calculation runs locally in your browser. The measurements, dates and details you enter stay on your own device and are never sent to a server — nothing is stored, logged or shared.

Frequently asked questions

What is lean body mass?
It is everything that is not fat: muscle, bone, organs and water. Tracking it helps you tell whether weight change is muscle or fat.
Why does lean mass matter?
Lean mass drives your metabolism and strength. When losing weight, keeping lean mass (with protein and resistance training) is the goal; when building, gaining it is.
How is lean body mass different from body fat?
They are two sides of the same total. Lean body mass is everything that is not fat, while body fat is the fat itself. Add the two together and you get your full body weight.

Important

These calculators give general, informational estimates and are not medical advice, diagnosis or treatment. Everyone is different — for decisions about your health, talk to a qualified clinician.

More tools

BMI CalculatorBody mass index, your category and a healthy weight range.Body Fat CalculatorBody fat percentage from the US Navy measurement method.Ideal Weight CalculatorA healthy target weight range for your height.Waist-to-Hip Ratio CalculatorWaist-to-hip ratio and your WHO health-risk band.BMR CalculatorCalories your body burns at rest (Mifflin-St Jeor).TDEE CalculatorTotal daily calories burned, from BMR and activity.

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