CALCULATOR 15
Lean Body Mass Calculator
Everything you weigh that isn't fat, estimated three ways, plus your fat-free mass index.
Lean body mass
Choose the sex used in the formulas.
For general information only; not medical advice. Consult a qualified professional before making health decisions.
How this is calculated
Boer (default), W = weight in kg, H = height in cm
Men: 0.407 W + 0.267 H − 19.2 Women: 0.252 W + 0.473 H − 48.3
James
Men: 1.1 W − 128 (W ÷ H)² Women: 1.07 W − 148 (W ÷ H)²
Hume
Men: 0.32810 W + 0.33929 H − 29.5336 Women: 0.29569 W + 0.41813 H − 43.2933
From body fat %
Lean mass = weight × (1 − body fat % ÷ 100)
Fat-free mass index
FFMI = lean mass ÷ height (m)² Normalised FFMI = FFMI + 6.1 × (1.8 − height in m)
The formulas estimate lean mass from height and weight alone, so they can't tell a muscular person from a heavier one. Adding your body fat % gives a better estimate.
James's formula breaks down at high BMI; when it gives an impossible value it's left out.
Sources
- Boer P (1984), Am J Physiol 247:F632–F636; James WPT (1976), Research on obesity, HMSO; Hume R (1966), J Clin Pathol 19:389–391 — lean body mass formulas.
- Kouri EM et al. (1995), Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med 5:223–228.
About the lean body mass calculator
What lean body mass is
Lean body mass is your weight minus your fat: muscle, bone, organs, skin and water. It drives most of your resting calorie burn, which is why the Katch-McArdle BMR formula and protein targets for people with high body fat are based on it.
Read more about the Lean Body Mass calculator
Formulas or body fat %
Boer, James and Hume predict lean mass from height and weight, and were developed largely for medical uses such as drug dosing. They're reasonable for average builds but underestimate lean mass in muscular people. If you know your body fat %, from a tape-measure estimate or a scan, the calculator uses that instead.
FFMI: muscularity for your height
The fat-free mass index is like BMI for lean mass only, and the normalised version adjusts it to a height of 1.8 m so people of different heights compare fairly. Most untrained men sit around 17–20. In a 1995 study of strength athletes, drug-free men rarely exceeded 25.
Frequently asked questions
How do I calculate lean body mass?
The simplest way is weight × (1 − body fat %). Without a body fat %, formulas like Boer's estimate it from height and weight.
What is a good FFMI?
For men, around 18–20 is typical and 22+ is quite muscular. Drug-free men rarely exceed a normalised FFMI of 25. Women's values are usually about 3–4 points lower.
Is lean body mass the same as muscle mass?
No. Lean mass includes muscle plus bone, organs, skin and water. Muscle is usually around half of it.
Which lean body mass formula is most accurate?
Boer's formula is often the closest for average builds, so it's the default. A body fat measurement beats all three formulas.