What this calculator does
Lean body mass is everything that is not fat: muscle, bone, organs and body water. The Boer formula estimates it from height and weight alone, which is crude but requires no measurement beyond what most people already know.
Because it depends mostly on height, adding weight adds mostly fat in the model. A 175 cm man is estimated at 51.9 kg lean at 60 kg body weight and 66.2 kg lean at 95 kg, so the extra 35 kg is treated as roughly 40 per cent lean tissue.
The formula
Separate regression equations for men and women combine weight and height with fitted coefficients. Fat mass is body weight less the lean estimate.
| Term | Meaning |
|---|---|
| Lean body mass | Total body mass excluding fat. |
| Boer formula | One of several published regressions, fitted to body composition measurements. |
| Fat mass | Body weight less lean body mass. |
The inputs explained
| Field | What to enter |
|---|---|
| Weight (kg) | Body weight in kilograms. |
| Height (cm) | Height in centimetres. |
| Sex | Sex, which selects between the two fitted equations. |
When to use it
Dosing a medication by lean mass
Some drugs distribute through lean tissue rather than total body weight, which matters in anaesthesia.
Setting a protein target
Protein recommendations are sometimes expressed per kilogram of lean mass rather than total weight.
Providing a rough baseline
A starting estimate where body composition measurement is not available.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does weight change the lean estimate?
The same height at three body weights.
Questions
How accurate is this?
It is a population regression from height and weight, with no knowledge of your actual build. A heavily muscled person and a sedentary person of the same height and weight receive identical estimates, which is clearly wrong for at least one of them.
How do I measure it properly?
DEXA scanning is the usual reference standard, with bioelectrical impedance and skinfold measurement as more accessible alternatives. All of them measure something; a formula from height and weight only infers it.
Why are there separate equations for men and women?
Because average body composition differs, with women typically carrying a higher proportion of fat at the same height and weight. The two equations reflect that average, not any individual.
Which formula is best?
Boer, James and Hume are the common alternatives and they disagree with one another, particularly at the extremes of body size. None is clearly best, which is itself a reason to treat any of them as approximate.
For body composition as a percentage, see the body fat calculator. For water content, see the total body water calculator.