Lean body mass calculator
Enter your height and weight, estimate your lean mass.
What is lean body mass?
Everything in the body except fat: muscle, bone, organs and water. Some drug doses and nutrition plans use it instead of total weight.
How is lean body mass calculated?
From height and weight with formulas fit to measured groups. The Boer formula for men is 0.407 × weight (kg) + 0.267 × height (cm) − 19.2: 80 kg and 180 cm give 61.4 kg.
Why are there three results?
Boer (1984), James (1976) and Hume (1966) were built from different groups of people, so they differ by a few pounds. None is exact for one person.
How does this relate to body fat?
Body fat % ≈ (weight − lean mass) ÷ weight. For a precise measurement, methods such as DEXA scans are used.
Does it work for very muscular or very heavy people?
Less well — the formulas only use height and weight, so they cannot tell muscle from fat.
What is the difference between lean body mass and fat-free mass?
The terms are often used as synonyms. Strictly, lean body mass can include a small amount of essential fat in the bone marrow, brain and organs, while fat-free mass has no fat at all, so fat-free mass is slightly smaller. The three formulas here estimate lean body mass from height and weight and do not separate the two.
Why do the formulas use height as well as weight?
Because two people of the same weight but different heights carry different amounts of lean tissue. A taller person has a larger skeleton and more organ and muscle mass for the same scale weight, so the Boer and Hume formulas add a term for height, and the James formula uses the weight-to-height ratio.
Can I use this for drug dosing?
Not on its own. Lean-mass-based dosing is done by clinicians with the formula and units their reference specifies, and the three estimates here can differ by several kilograms. Use the figure to understand body composition, and take dosing questions to a pharmacist or physician.
The three formulas
All three take weight W in kilograms and height H in centimeters, with separate versions for men and women. Boer (1984): men 0.407 W + 0.267 H − 19.2, women 0.252 W + 0.473 H − 48.3. Hume (1966): men 0.3281 W + 0.33929 H − 29.5336, women 0.29569 W + 0.41813 H − 43.2933. James (1976) is nonlinear: men 1.1 W − 128 (W/H)², women 1.07 W − 148 (W/H)². The implied body fat is simply (weight − lean mass) ÷ weight, so it inherits every error in the lean mass estimate. The calculator converts pounds and inches for you and returns pounds or kilograms to match the units you pick.
Worked example: 65 kg, 165 cm, woman
A woman weighing 65 kg (143.3 lb) and 165 cm tall gets these lean mass values: Boer (1984) 46.1 kg (101.7 lb, 29.0% implied body fat); James (1976) 46.6 kg (102.7 lb, 28.3% implied body fat); Hume (1966) 44.9 kg (99.0 lb, 30.9% implied body fat). For Boer, 0.252 × 65 + 0.473 × 165 − 48.3 = 46.1 kg. The three answers span 1.7 kg, so the implied body fat ranges by 2.6 percentage points from one formula to the next. That spread is a fair picture of the uncertainty of height-and-weight methods.
Things to watch
- Compare like with like. Switching formulas between measurements can look like a change in lean mass when it is only a change in method; track one formula over time.
- The James formula bends over. For a man 180 cm tall its estimate stops rising at about 139 kg of body weight and then falls, which makes no physical sense, so James is unreliable for very heavy people.
- Because only height and weight go in, gaining 5 kg of pure fat is reported as a gain in lean mass. Real body composition tests such as DEXA measure tissue directly.
- Weight must be entered in the unit shown on the active toggle; 65 read as pounds instead of kilograms gives a very different answer.
For general information only — not medical advice. Talk with your doctor or another health professional about your own health. How we check our calculators.
Sources: the original Boer (1984), James (1976) and Hume (1966) equations as tabulated in the clinical-pharmacology literature on lean body mass. Related tools: ideal weight calculator, body fat calculator, BMI calculator.