How lean body mass is estimated
The Boer equation uses weight and height to split your body into lean mass and everything else. For men it is 0.407 × kg + 0.267 × cm − 19.2; for women, 0.252 × kg + 0.473 × cm − 48.3. An 80 kg, 180 cm man lands at 61.4 kg. Compare with the ideal weight calculator for context. Subtract lean mass from total weight and you have the figure the body fat calculator reports as a percentage.
Why lean mass matters
Lean mass — muscle, bone, organs and water — drives your metabolism and strength. It is one reason the BMR calculator figures vary so much between people of the same weight. This is a general wellness estimate, not medical advice. Talk to a healthcare professional for personal guidance.
Lean tissue also stores glycogen and the water bound to it, which is why the scale can move two kilograms in a week with no real change in fat. Lean tissue drives energy use, which is why it appears in the BMR calculator.
Estimate versus measurement
This is a formula-based estimate. DEXA scans and hydrostatic weighing measure lean mass directly and are more accurate, but the Boer figure is a useful free starting point.
The Boer equation assumes an average build, so it under-reads for very muscular people and over-reads for someone carrying a lot of fat at the same weight. Tracking the number over time is more useful than any single reading: if your weight holds steady while estimated lean mass climbs, you are likely trading fat for muscle. This is a general wellness estimate, not medical advice. Protein targets are usually set from lean mass in the macro calculator.
Frequently asked questions
- What is lean body mass?
- It is everything in your body except fat — muscle, bone, organs and water.
- Which formula is used here?
- The Boer formula, which estimates lean mass from weight, height and sex.
- How accurate is it?
- It is a reasonable estimate for average builds; direct scans like DEXA are more precise.
- Why does sex change the result?
- On average men carry more muscle and less fat, so the equations differ by sex.
- How do I get my fat mass in kg from this?
- Subtract lean body mass from total weight. At 80 kg with 61.4 kg of lean mass, the remaining 18.6 kg is fat and other tissue. Dividing that by total weight gives a rough body fat percentage.