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Lean Body Mass Calculator

Estimate your lean body mass with the Boer, James and Hume formulas, or from your body fat %. Also shows fat mass and FFMI. Free LBM calculator.

Lean body mass (Boer)
49.8 kg
Boer formula
49.8 kg
James formula
49.8 kg
Hume formula
48.5 kg
Body fat (estimated)
28.9%
Fat mass
20.3 kg
Fat-free mass index
17.2

Lean body mass explained

Lean body mass is your weight minus your body fat: muscle, bone, organs and water. It's used for drug dosing, protein targets and tracking fitness. The Boer formula is the most widely used: for a 70 kg, 170 cm woman it gives 49.8 kg. If you know your body fat percentage from a scale or calipers, enter it for a direct figure: 70 kg at 25% fat is 52.5 kg lean. The fat-free mass index (FFMI) adjusts lean mass for height, like BMI does for weight.

How to use it

  1. 1

    Enter your details

    Sex, weight and height in metric or US units.

  2. 2

    Add body fat (optional)

    If you know it, for a direct calculation.

  3. 3

    Compare the formulas

    Boer, James and Hume, with fat mass and FFMI.

Frequently asked questions

What is the Boer formula?

Men: 0.407 × weight + 0.267 × height − 19.2. Women: 0.252 × weight + 0.473 × height − 48.3 (kg and cm).

What is a good FFMI?

About 18–20 is average for men and 14–17 for women. Above 25 is rare without years of training.

Lean body mass vs fat-free mass?

They're nearly the same; lean mass includes a small amount of essential fat.

Is my data stored?

No. The calculation runs in your browser.

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