What is the difference between lean body mass and fat-free mass?

Fat-free mass excludes all fat. Lean body mass technically includes the small amount of essential fat within organs and the nervous system. In practice the terms are used interchangeably.

Which lean body mass equation is best?

Boer is the most widely used general-purpose equation. If you have a reliable body fat measurement, use it instead of any prediction formula.

Why does lean body mass matter for calories?

Lean tissue is metabolically active, so it largely determines resting metabolic rate. The Katch-McArdle equation calculates BMR directly from lean mass.

How fast can lean mass increase?

With consistent resistance training and adequate protein, novices may add roughly 1-2 lb a month, and experienced lifters considerably less.

Lean Body Mass Calculator

Estimate lean body mass with the Boer, James and Hume equations.

Enter your details and your result will appear here.

What Is Lean Body Mass?

Lean body mass is everything in your body that is not fat: muscle, bone, organs, connective tissue and body water. This calculator estimates it from height, weight and sex using three published equations, and shows the fat mass that implies.

Understanding Your Lean Body Mass Result

Lean mass matters because it is the main driver of resting metabolic rate and the tissue that resistance training builds. Prediction equations exist because measuring lean mass directly needs DXA, hydrostatic weighing or a similar method. Each equation was fitted to a different population, which is why their results differ by a kilogram or two.

How Is Lean Body Mass Calculated?

Boer (male): LBM = 0.407 x weight (kg) + 0.267 x height (cm) - 19.2

Methodology

Boer (1984) is the default: for men, 0.407 x weight in kg + 0.267 x height in cm - 19.2; for women, 0.252 x weight + 0.473 x height - 48.3. The James (1976) and Hume (1966) equations are shown for comparison. Fat mass is total weight minus lean mass.

Worked Example

A woman who is 5 ft 6 in (167.6 cm) and 150 lb (68 kg) gets a Boer lean body mass of 0.252 x 68 + 0.473 x 167.6 - 48.3, or about 48.1 kg (106 lb). That implies roughly 44 lb of fat mass, or about 29% body fat.

Important Limitations

These equations use only height, weight and sex, so they cannot see how muscular you are. A trained lifter will be underestimated and a sedentary person of the same size overestimated. If you have a measured body fat percentage, lean mass calculated as weight x (1 - body fat percentage) is more accurate than any of these formulas.

Frequently Asked Questions

What is the difference between lean body mass and fat-free mass?: Fat-free mass excludes all fat. Lean body mass technically includes the small amount of essential fat within organs and the nervous system. In practice the terms are used interchangeably.
Which lean body mass equation is best?: Boer is the most widely used general-purpose equation. If you have a reliable body fat measurement, use it instead of any prediction formula.
Why does lean body mass matter for calories?: Lean tissue is metabolically active, so it largely determines resting metabolic rate. The Katch-McArdle equation calculates BMR directly from lean mass.
How fast can lean mass increase?: With consistent resistance training and adequate protein, novices may add roughly 1-2 lb a month, and experienced lifters considerably less.