Lean Body Mass Calculator: Boer, James, Hume, Peters
Estimate lean body mass from sex, age, weight and height with the Boer, James and Hume formulas side by side, or the Peters formula for children under 14. Shows kg, lb and implied body fat. Nothing is uploaded.
Enter your age, weight and height to see your lean body mass.
About the Lean Body Mass Calculator
The Lean Body Mass Calculator estimates your lean body mass: everything in the body that is not fat, including muscle, bone, organs, skin and body water. Enter your sex, age, weight and height in metric or US customary units. For anyone aged 14 or over, the calculator shows the Boer, James and Hume formulas side by side, because they were fitted to different groups of people and give slightly different answers. For children under 14 it uses the Peters formula, which was developed for children. Each estimate is shown in kilograms and pounds, together with the body fat percentage it implies.
This is an estimate, not medical advice. The formulas predict the average lean mass of people with your height and weight; a muscular person will have more lean mass than predicted and a sedentary person less. A DEXA scan or a clinician can measure your own lean mass.
How to use it
Steps
- Choose your sex and your units.
- Enter your age, weight and height.
- Compare the estimates in the table. The implied body fat is the share of your weight that each formula leaves over after lean mass.
Which formula
The Boer formula is often preferred in clinical work and drug dosing for adults of normal build. The James formula is widely used but gives implausible values for people with a high BMI, because its squared term makes the estimate fall as weight rises; the calculator marks such a result as out of range. The Hume formula sits close to the other two for most adults.
The formulas
With weight W in kilograms and height H in centimetres:
For children, Peters and colleagues first estimate the extracellular fluid volume and then scale it to lean mass, for either sex:
Worked example
For a man who weighs 80 kg and is 180 cm tall, Boer gives 61.4 kg, James 62.7 kg and Hume 57.8 kg. The Boer value implies a body fat of 23.2 %. A 10-year-old who weighs 30 kg and is 130 cm tall has an estimated lean mass of 25 kg by the Peters formula.
Privacy
Nothing is uploaded: every calculation runs in your browser and your measurements never leave your device.
Related tools
Estimate body fat from tape measurements with the Body Fat Calculator, check your body mass index with the BMI Calculator, or work out body surface area with the Body Surface Area Calculator. The Mass Converter converts between kilograms and pounds.
Sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. American Journal of Physiology 1984; 247: F632–F636.
- James W.P.T. Research on Obesity: a report of the DHSS/MRC group. HMSO, London, 1976.
- Hume R. Prediction of lean body mass from height and weight. Journal of Clinical Pathology 1966; 19: 389–391.
- Peters A.M., Snelling H.L., Glass D.M., Bird N.J. Estimation of lean body mass in children. British Journal of Anaesthesia 2011; 106: 719–723.
Open-source credits
The calculations are implemented in-house in TypeScript, with no third-party library. They follow the published Boer, James, Hume and Peters lean body mass formulas listed above.
Frequently asked questions
What is lean body mass?
Lean body mass is your total weight minus the weight of body fat. It includes muscle, bone, organs, skin, blood and body water. It is used in medicine to dose some drugs and anaesthetics, and in nutrition to estimate protein and energy needs.
Why do the three formulas give different results?
Boer, James and Hume each fitted their equations to a different group of people, measured with different methods, so they disagree by a few kilograms. None of them is exact for one person. Showing them side by side gives a sense of the likely range.
Why does the James formula sometimes show out of range?
The James formula subtracts a term that grows with the square of weight divided by height. At a high BMI that term grows faster than the rest, so the estimate falls as weight rises and can even become negative. The calculator marks any estimate of zero or less, or one at least as large as the weight, as out of range.
Why is there a separate formula for children?
The adult formulas were fitted to adults and give poor results for children, whose body proportions and water content differ. Peters and colleagues developed a formula from children's measurements in 2011, so the calculator uses it for anyone under 14.