Lean Body Mass Calculator
Lean body mass is everything that is not fat — muscle, bone, organs, water. It is the figure several other calculations scale to.
Your results
Only as accurate as the body-fat figure you feed it. The Boer estimate ignores your actual composition entirely and can be several kilograms out for muscular people.
Why lean mass matters
Several things scale better to lean mass than to total weight:
- Protein requirements in a deficit, where the recommendation is stated per kg of fat-free mass.
- Katch-McArdle BMR, which uses lean mass directly.
- FFMI, the muscularity index that BMI cannot provide.
It is also the number you want to hold during a diet. Losing weight while lean mass stays flat is exactly the goal.
The Boer formula
When body fat is unknown, the Boer formula estimates lean mass from height and weight:
- Men: (0.407 × kg) + (0.267 × cm) − 19.2
- Women: (0.252 × kg) + (0.473 × cm) − 48.3
It assumes average body composition, so it under-estimates lean mass in muscular people and over-estimates it in people carrying more fat. Use the body-fat route where you can.
Common questions
What is a normal lean body mass?
It depends almost entirely on height and training history. The useful comparison is against your own figure over time, not against a population.
Should lean mass stay the same while dieting?
That is the goal. Heavy training and high protein keep the loss mostly fat.
Is lean body mass the same as muscle mass?
No — it includes bone, organs and water. Skeletal muscle is roughly half of it.
How do I increase lean mass?
Resistance training with progressive overload, adequate protein, and a small calorie surplus.
Related calculators
Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
