Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Estimate lean body mass and fat mass using the Boer formula.
Lean body mass (LBM) is your total body weight minus fat mass -- muscle, bone, organs, water. This tool estimates it using the Boer formula (1984), commonly cited as the most accurate of the classic LBM equations for a general population.
Enter your weight, height, and sex. Estimated lean mass and fat mass both appear instantly.
Men: LBM = 0.407 × weight(kg) + 0.267 × height(cm) - 19.2
Women: LBM = 0.252 × weight(kg) + 0.473 × height(cm) - 48.3
Lean body mass is a common input for the Fat-Free Mass Index Calculator (height-normalized muscularity), and some protein-intake guidance is based on lean mass rather than total weight for more precision.
Consider a hypothetical man who weighs 80 kg and is 180 cm tall, which are the values the calculator opens with. The Boer equation gives 0.407 times 80, which is 32.56, plus 0.267 times 180, which is 48.06, minus 19.2. The lean body mass is about 61.4 kg. The tool then subtracts this from total weight to show a fat mass of about 18.6 kg. That is roughly 23 percent of his body weight. For a hypothetical woman who weighs 65 kg and is 165 cm tall, the female equation gives about 46.1 kg of lean mass and therefore about 18.9 kg of fat mass.
Fat mass = body weight - lean body mass
The tool shows two tiles, lean mass and fat mass, both in kilograms with one decimal place. They always add up to your entered weight, because fat mass is calculated by subtraction rather than measured independently. That means any error in the lean mass estimate goes straight into the fat mass figure. Also note that the equation depends on height and weight but not on age or on any body measurement, so two people of the same sex, height and weight will get identical results even if their bodies are very different.
Lean mass includes muscle, bone, organs and body water, so it does not equal muscle. If you gain muscle through training, this tool will not necessarily show it, since it only sees your weight and height. Use it as a rough reference to compare with other estimates, such as circumference-based body fat, or as an input for planning tools like protein guidance, as long as you understand it is a formula and not a measurement. Body composition scans such as DEXA, and clinical assessments, give direct readings.
If you have concerns about your weight, muscle or nutrition, speak with a doctor or registered dietitian. This calculator is educational only and is not medical advice.
No -- LBM includes muscle plus bone, organs, and water; it's everything that isn't fat, not muscle alone.
It's one of the more accurate classic prediction equations, but like all such formulas it's an estimate, not a direct measurement (which would require a DEXA scan or similar).
Yes -- some sports-nutrition guidance bases protein targets on lean mass rather than total weight; see the Protein Intake Calculator for a total-weight-based approach.
The Boer equation uses only sex, weight and height. It cannot see age, training history, or how fat and muscle are distributed.
No. It is your weight minus the estimated lean mass, so any error in the lean estimate carries directly into the fat mass.
For unusual combinations of weight and height it can, because the equation is a regression. That signals the formula does not suit those inputs.
Only through the weight you enter. The tool cannot detect body composition changes when weight and height stay the same.
Reference: Centers for Disease Control and Prevention