Lean body mass calculator
Enter your sex, height and weight to estimate your lean body mass – everything that is not fat – with three published formulas. The results are close but not identical, so compare them rather than trusting a single figure.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose your units and sex.
- Enter your weight and height.
- Compare the three lean mass estimates and the body fat percentage each one implies.
With weight W in kilograms and height H in centimetres:
| Formula |
Men |
Women |
| Boer (1984) |
0.407 W + 0.267 H − 19.2 |
0.252 W + 0.473 H − 48.3 |
| James (1976) |
1.10 W − 128 (W ÷ H)² |
1.07 W − 148 (W ÷ H)² |
| Hume (1966) |
0.3281 W + 0.33929 H − 29.5336 |
0.29569 W + 0.41813 H − 43.2933 |
Pounds and feet/inches are converted to kilograms and centimetres first (1 lb = 0.45359237 kg, 1 in = 2.54 cm). Implied body fat is (1 − lean mass ÷ weight) × 100; it is left blank if the formula gives a lean mass outside 0 to your weight.
Worked example
A man weighing 70 kg and 175 cm tall. Boer: 0.407 × 70 + 0.267 × 175 − 19.2 = 56.0 kg. James: 1.10 × 70 − 128 × (70 ÷ 175)² = 77 − 20.48 = 56.5 kg. Hume: 0.3281 × 70 + 0.33929 × 175 − 29.5336 = 52.8 kg. By Boer, body fat is (1 − 56.0 ÷ 70) × 100 ≈ 20 %.
Limits
- The formulas were derived for adults of typical build; they are less reliable for very muscular, very lean, elderly or pregnant people and for children.
- They use only height, weight and sex, so two people with the same numbers get the same result whatever their fitness.
- This is general information, not medical advice.
Frequently asked questions
What is lean body mass?
It is your total body weight minus the weight of body fat. It includes muscle, bones, organs, skin and body water. It is not the same as muscle mass, which is only a part of it.
Which formula is the most accurate?
None is a measurement. All three were fitted to groups of people and give averages for someone of your height and weight; individual error of several kilograms is normal. The James formula can behave oddly at very high weights, so it is best compared with the others.
Why are my three results different?
Each formula was built from a different group of people with a different method. They agree on the order of magnitude, and a spread of a few kilograms is expected. Using the same formula over time is more useful than choosing the single best one.
Is the body fat percentage here reliable?
It is only 1 − lean mass ÷ weight, so it is as rough as the formula. Methods that measure the body, such as DEXA, or a tape measure method such as the Navy method in our body fat calculator, give a more direct estimate.
What is lean body mass used for?
Doctors use it to scale some drug doses and body fluid volumes, and fitness people use it to set protein targets or to follow a diet. It is a planning figure, not a health score.