How this lean body mass calculator works
We give you up to three estimates. All of them use your weight in kilograms and height in centimeters behind the scenes, so you can enter pounds, stone, or kilograms.
From your body fat %. If you enter body fat, this becomes your main result:
Lean mass = weight × (1 − body fat % ÷ 100)
Boer (1984). If you leave body fat blank, this is your main result. It only needs sex, height, and weight.
- Men: 0.407 × weight + 0.267 × height − 19.2
- Women: 0.252 × weight + 0.473 × height − 48.3
Hume (1966). A second height and weight formula, shown for comparison.
- Men: 0.32810 × weight + 0.33929 × height − 29.5336
- Women: 0.29569 × weight + 0.41813 × height − 43.2933
Your result also shows lean mass as a percent of your total weight.
What your result means
Lean mass is what's left after you take away fat. If your lean mass goes up over time while your weight stays the same, you've likely swapped some fat for muscle. If you're losing weight, keeping your lean mass steady is a good sign that most of the loss is fat.
The Boer and Hume numbers are averages for someone of your size and sex. They can't see whether you lift weights. If you're quite muscular, they may come in low. The body fat method is more personal, but it's only as good as the body fat number you give it.
How to use your lean mass
- Protein: Eating enough protein and doing strength training help you keep lean mass while you lose fat. Our protein calculator sets a daily target.
- Calories: Your lean mass feeds the Katch-McArdle equation in our BMR calculator.
- Muscle: Divide lean mass by height squared and you get FFMI. Try our FFMI calculator.
Don't know your body fat? Get an estimate with our body fat calculator. For a fuller explanation, read our guide, what is lean body mass.