How lean body mass is estimated
The Boer formula estimates the weight of everything in your body except fat — muscle, bone, organs, and water — from your total weight and height. Subtracting it from your weight gives an estimated fat mass.
- kg — body weight in kilograms
- cm — height in centimeters
- LBM — lean body mass (kg)
More detail
Why sex changes the formula
Men typically carry more muscle and bone mass relative to weight than women at the same height, so the Boer formula uses a higher weight coefficient (0.407 vs. 0.252) and a lower constant offset for men. This is a population average — individual body composition can differ substantially, especially for athletes.
Practical tip. LBM is a proxy for muscle+bone+organ mass, not a direct measurement — DEXA scans or bioelectrical impedance scales give more accurate individual readings. Use this as a rough starting point, and track trends over time rather than a single number.
Frequently asked questions
What's a normal lean body mass for my weight?
There's no single "normal" — LBM scales with height and sex. The Boer formula above gives 0.407 × kg + 0.267 × cm − 19.2 for men and 0.252 × kg + 0.473 × cm − 48.3 for women; enter your numbers for your estimate.
How is lean body mass different from fat-free mass?
They're often used interchangeably, but strictly lean body mass includes a small amount of essential fat (in organs and cell membranes), while fat-free mass excludes all fat. The difference is usually only 2-3% of body weight, so the Boer formula's LBM output is commonly treated as fat-free mass in practice.
Why does the Boer formula give a different answer than a body-fat scale?
The Boer formula (1984) is a statistical estimate from height, weight, and sex alone — it doesn't measure your actual tissue. Bioelectrical impedance scales and DEXA scans measure your body directly and are more accurate for an individual, though results can vary with hydration and time of day.
Can lean body mass be higher than my total weight?
No — if the formula puts body fat below this calculator's display floor (6% male / 14% female) — which happens before lean mass ever reaches your entered weight (most often at tall, lean builds, since the equation is linear), the estimate isn't meaningful for that input. It is a limit of the formula, not a mistake in your input.