Enter your sex, height, and weight — the Boer formula estimates lean body mass, with fat mass and implied body fat % derived from the remainder.
Run the page's own default measurements — 178 cm, 80 kg — through the female coefficients instead of the male ones and the estimate moves substantially: LBM = 0.252 × 80 + 0.473 × 178 − 48.3 ≈ 56.05 kg, versus 60.89 kg for a man at the identical height and weight. That is an implied body fat of 29.9% against 23.9% — nearly 6 percentage points apart, from the same two numbers, purely because the Boer formula fits male and female body composition on separate curves rather than one universal one.
This page's own default works out to a fat mass of 19.11 kg on an 80 kg frame — an implied body fat of 23.9%. That percentage is exactly the input the Protein Calculator's "lean body mass" basis wants: enter the same total weight and that percentage there, and it scales a daily protein target (commonly 1.6–2.2 g per kg for muscle-building goals) to lean tissue specifically rather than to total body weight, which matters most for someone carrying more fat than average.
The Boer formula was fitted against a general adult population, so it assumes a fairly typical ratio of muscle to frame size for a given height. Someone considerably more muscular than average — a bodybuilder or strength athlete — will usually have their lean mass underestimated by a formula like this, since it has no way to detect unusually dense muscle mass from height and weight alone. The Body Fat Calculator's circumference-based method is less easily fooled by build outliers, since it measures actual body shape rather than inferring it from two numbers — and the BMI Calculator shows the simplest version of that same trade-off, with no sex adjustment at all.
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.
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.
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.
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%.
Mixing units. Most lean-mass formulas were published in kilograms while a lot of the equipment reporting body weight is calibrated in pounds, and converting at the wrong point is a common source of nonsense results. Convert your weight first with the kg to pounds converter, then enter a single consistent unit here rather than converting the answer afterwards.
See the Body Fat Calculator for a direct circumference-based estimate, or the Protein Calculator to size your daily protein target from lean mass. Muscle mass is exactly why creatinine-based kidney estimates can mislead — the eGFR Calculator explains when. See also the Body Surface Area Calculator.