Lean Body Mass Calculator

Your lean body mass is everything you are made of except fat: your muscle, bone, organs and body water added together. It is a far more meaningful number than body weight alone, because two people can weigh exactly the same while having very different amounts of muscle and fat, and it is the figure that really moves when training and nutrition are working. This calculator estimates your lean body mass, and the fat mass that makes up the rest of your weight, from just your weight, height and sex, using the well established Boer formula. Enter your details and it returns your lean mass in kilograms, your fat mass, and your body fat percentage, giving you a simple snapshot of your body composition without needing a scan or special equipment. People use lean body mass for all sorts of practical reasons: setting a daily protein target, since protein needs are often based on lean mass rather than total weight; tracking real progress on a fitness or fat-loss programme, where the goal is usually to hold or build lean mass while fat comes down; and as background context for general health. Because it updates instantly, you can see how a change in weight at the same height shifts the split between lean and fat mass. It is important to remember that this is an estimate from a population formula, not a direct measurement like a DEXA scan, so treat the numbers as a useful guide and a way to watch trends over time rather than an exact reading. The method and a worked example are explained below.

Estimated with the Boer formula from weight and height. An estimate from a population formula, not a direct measurement, and not medical advice. For body composition that matters clinically, see a health professional.