Lean Body Mass Calculator
Your scale tells you total weight — but not how much of it is muscle versus fat. This lean body mass calculator uses the Boer formula to estimate your LBM, fat mass, and body fat percentage from just weight and height.
Enter your numbers
Your results
Estimates from the Boer formula — fine for tracking trends, not a medical measurement. A DEXA scan gives a more precise reading.
How to use this calculator
Pick metric or imperial, choose your sex, and enter weight and height. Results update instantly — no button press needed.
Example: a man weighing 80 kg at 180 cm tall has an estimated lean body mass of 61.42 kg, which means about 18.58 kg of fat mass, or 23.2% body fat.
How it works
The Boer formula estimates lean body mass from weight (w, in kg) and height (h, in cm):
Men: LBM = 0.407 × w + 0.267 × h − 19.2
Women: LBM = 0.252 × w + 0.473 × h − 48.3
Estimated body fat % = (1 − LBM ÷ weight) × 100, and fat mass = weight − LBM. Imperial inputs are converted internally (1 lb = 0.45359237 kg, 1 in = 2.54 cm) before the formula runs. Because the formula only knows weight, height, and sex — not where your fat is stored — treat the result as an estimate.
Frequently asked questions
What is lean body mass?
Lean body mass (LBM) is everything in your body that is not fat: muscle, bone, organs, and water. Subtracting it from total weight gives your fat mass.
How accurate is the Boer formula?
The Boer formula is a widely used estimate based on weight, height, and sex, typically within a few percent of clinical measurements. For precision, a DEXA scan is better; for tracking trends over time, the formula works well.
Why are there separate formulas for men and women?
Men and women distribute body composition differently at the same height and weight - on average, women carry a higher percentage of essential body fat, so the formula coefficients differ.
Is lean body mass the same as fat-free mass?
In practice the terms are used interchangeably. Technically, fat-free mass excludes all fat while lean body mass includes a small amount of essential fat, but the difference is negligible for everyday tracking.