The formula
How it works
Lean body mass is everything in your body that is not fat — muscle, bone, organs and water. This calculator estimates it from your height, weight and sex using the Boer formula, and shows the fat mass that makes up the rest.
FAQ
What counts as lean body mass?
Everything except stored fat: muscle, bone, connective tissue, organs and the water in your body. It is sometimes called fat-free mass.
Why does lean mass matter?
Muscle burns more calories than fat and drives strength, so tracking lean mass helps make sure a diet loses fat rather than muscle. Medicine also uses it to set some drug doses.
How accurate is the Boer formula?
It is a well-tested estimate based on population averages, but it does not account for individual differences in muscle or bone density, so it can be off for very lean, very heavy, or highly muscular people. Direct body-composition measurements are more precise.
How is lean body mass different from BMI?
BMI only compares weight to height and cannot tell muscle from fat, so a muscular person can score as “overweight”. Lean body mass instead estimates how much of your weight is fat-free, giving a more meaningful picture of body composition.
Why might the calculator show a low or zero result?
The Boer formula can produce an unrealistic estimate for very short or very light inputs, since it subtracts a fixed constant from the weight and height terms. The calculator floors the result at zero rather than showing a negative number.
How can I increase my lean body mass?
Resistance training paired with enough dietary protein is the main way to build and preserve muscle, which is the biggest component of lean mass you can change. Consistency over weeks and months matters more than any single workout or meal.
What other methods measure lean body mass more precisely?
DEXA scans, bioelectrical impedance devices, and hydrostatic (underwater) weighing all measure body composition directly rather than estimating it from height and weight, and are generally more accurate than formula-based methods like this one.
About the lean body mass calculator
This calculator estimates your lean body mass — the weight of everything in your body other than fat. Lean mass includes your muscles, bones, organs and body water, and it is a more meaningful number than total weight for anyone tracking fitness or health. Knowing roughly how much of your weight is lean tissue, and how much is fat, gives a clearer picture than the scale alone.
How to use it
Choose your sex and units, then enter your height and weight. The calculator returns your estimated lean body mass, along with your fat mass and the share of your weight that is lean. For example, an 80 kg man of 180 cm has a lean mass of about 61 kg, leaving roughly 19 kg of fat. Because the estimate is based on averages, treat it as a guide and watch how it changes rather than fixating on the exact figure.
The formula
This uses the Boer formula. For men, , and for women , where is weight in kilograms and is height in centimetres. Imperial inputs are converted to metric first. Fat mass is then simply your total weight minus the lean body mass, and dividing lean mass by weight gives the lean percentage.
Where it is used
Lean body mass is used in medicine to work out doses of drugs and anaesthetics that should be scaled to lean tissue rather than fat, and to set nutrition for patients. In fitness, it helps athletes and dieters make sure weight changes are the right kind — losing fat while keeping muscle. Sports scientists track it to measure training gains, and it underpins more detailed body-composition measures.