Lean Body Mass Calculator

Lean body mass is your total body weight minus body fat: muscle, bone, organs, and water. It’s a useful baseline for tracking strength and metabolic changes over time, and it’s the input several other calculators on this site build on, most directly the Katch-McArdle path in the TDEE Calculator.

What This Calculator Measures

This estimates lean mass from height and weight alone, without requiring a body fat measurement. If you already know your body fat percentage, that’s a more direct route to the same number, since lean mass is simply your weight times one minus your body fat fraction.

The Formula

This calculator uses the Boer formula¹, developed from a Dutch adult sample and still one of the most widely used height-weight equations for lean mass in clinical settings.

Men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2

Women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3

How This Calculator Computes Your Result

Enter your sex, height, and weight above. We run the Boer formula directly and also report estimated fat mass as the remainder of your total body weight.

How Boer Compares to Other Formulas

Boer isn’t the only height-weight equation for lean mass. An earlier formula developed from a British sample² tends to produce noticeably lower estimates at typical modern body weights. In the worked example below it comes in 3.6 kg under Boer for the man and 1.2 kg under for the woman.

A more recent equation built from a much larger dataset spanning normal-weight through severely obese adults³ explicitly accounts for the fact that, at very high body weights, additional weight is overwhelmingly fat rather than lean tissue, something the older linear formulas don’t capture. Height-weight formulas are known to be inconsistent at the extremes of body size³.

The Three Formulas Side by Side

Weight is in kilograms and height in centimeters. BMI is weight ÷ height in meters squared.

Worked Example

Take a man who is 180 cm and 80 kg. Boer gives 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg of lean mass. The calculator then reports fat mass as the remainder: 80 − 61.4 = 18.6 kg. Here is how the three formulas compare for him and for a woman who is 165 cm and 65 kg:

For these two typical adults the formulas land within about 4 to 5 kg of each other. That spread is a useful reminder that any single result is an estimate. If you use imperial units, the calculator converts your entries to kilograms and centimeters, runs Boer, and converts the result back to pounds, shown to one decimal place.

Lean Body Mass vs Fat-Free Mass

The two terms are often used interchangeably. When the term lean body mass was introduced in 1942, it was described as including a small amount of "essential" structural fat, while fat-free mass was meant to contain no fat at all⁴. A 2024 review concluded that, as fat-free mass is actually measured, it already includes those structural lipids, so the two are chemically the same, and it recommends using the term fat-free mass⁴.

In practice, body composition methods such as DEXA measure fat-free mass, and there is no separate reference method for lean body mass³. So the lean mass you get from a body fat percentage, as described above, is really fat-free mass, and you can compare it directly with this estimate. Fat-free mass is also the starting point for the FFMI Calculator, which adjusts it for height.

Why It Matters

Two people can weigh the same yet have very different body composition. Tracking lean mass alongside weight shows whether changes come from muscle or fat. This is a formula-based estimate, and DEXA scans or BIA scales are more precise.