How much of your weight is lean mass?

What is lean body mass?

Lean body mass is your total body weight minus fat mass — it includes muscle, bone, organs, water, and everything else that isn't fat tissue. It's a useful reference point for nutrition and training since protein needs and resting metabolic rate track more closely with lean mass than with total body weight, which is why two people of the same weight can have quite different nutritional requirements.

How is this different from body fat percentage?

The Body Fat Calculator measures the fat portion directly from circumference measurements (neck, waist, and hip). This tool instead estimates lean mass from height and weight using the Boer formula, then derives fat mass as the remainder — so the two approaches can disagree slightly since they estimate different things from different inputs. For most people, the circumference-based body fat method is considered the more direct estimate of the two.

What formula does this use?

The Boer formula, a widely cited height-and-weight-based estimate of lean body mass: men: LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2, women: LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. Other formulas exist, including James and Hume, which use slightly different coefficients and can produce modestly different results for the same inputs — none is universally considered the single correct answer, so treat any of them as an estimate rather than a precise measurement.

Why does lean mass matter for fitness or nutrition?

Protein intake recommendations, calorie needs, and strength-training progress are often better tracked against lean mass than total body weight, since muscle is metabolically active tissue while fat largely isn't. See the Protein Calculator to translate your lean mass estimate into a daily protein target for muscle maintenance or growth.

Worked example: a man 178 cm tall weighing 80 kg: LBM = 0.407 × 80 + 0.267 × 178 − 19.2 = 32.56 + 47.53 − 19.2 ≈ 60.89 kg. Fat mass = 80 − 60.89 = 19.11 kg, an implied body fat percentage of 19.11 ÷ 80 × 100 ≈ 23.9%.