Lean Body Mass Calculator
Lean body mass from the Boer formula, with implied fat mass.
Lean Body Mass Calculator
| Lean body mass | 61.4 kg |
| Fat mass (weight − LBM) | 18.6 kg |
| Implied body fat | 23.2% |
An 80 kg man at 180 cm has a Boer lean body mass of 61.4 kg, implying 18.6 kg of fat mass — about 23.2% body fat.
Lean body mass (LBM) is everything in your body that is not fat — muscle, bone, organs and water. This calculator uses the Boer formula (1984), which estimates LBM from sex, weight and height and is widely used in clinical practice alongside the Hume formula.
Subtracting LBM from total weight gives fat mass and an implied body-fat percentage. The Boer estimate treats all non-fat tissue as one compartment and is a general estimate, not a body-composition measurement — DEXA or the Navy tape method will differ somewhat. Educational information only, not medical advice.
The formula
Worked example
An 80 kg man at 180 cm has a Boer lean body mass of 61.4 kg, implying 18.6 kg of fat mass — about 23.2% body fat.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
How is lean body mass different from fat-free mass?
They are close cousins: fat-free mass excludes all fat, while lean body mass includes a small amount of essential fat in organs and cell membranes. In practice the terms are often used interchangeably outside research.
Why does LBM matter for nutrition?
Protein targets, drug dosing and metabolic rate all track lean mass better than total weight. Two people at 90 kg can have very different needs if one carries 65 kg of lean mass and the other 50 kg.
Category: Health & Fitness calculators