Lean Body Mass (LBM)

Calculate your Lean Body Mass (weight minus fat)

Last updated: 10/8/2026

Lean body mass is everything you weigh that is not fat: muscle, bone, organs, blood, and water. It changes much more slowly than total weight, which makes it a steadier reference for protein targets, drug dosing in clinical settings, and judging whether a diet is costing muscle. This calculator needs your body weight and a body fat percentage; it returns lean mass and fat mass in the unit you entered.

Calculator Inputs

Body Weight*

Weight Unit*

Body Fat Percentage*

Results

Enter values above to see your results

The result inherits whatever error is in the body fat percentage you enter; consumer scales and tape methods can be several points off. Lean body mass is not a measure of health on its own and does not replace medical assessment.

How It Works

Fat mass = weight × body fat % ÷ 100. Lean body mass = weight − fat mass. The result is only as accurate as the body fat percentage you enter: this calculator does not estimate body fat itself. If you do not have a measured figure, the Body Fat Calculator (US Navy tape method) gives an estimate you can use here.

Where the body fat figure comes from matters

DEXA scans and hydrostatic weighing are accurate to within about 1 to 2 percentage points. Consumer bioimpedance scales can be off by 3 to 5 points and swing with hydration from one morning to the next. Tape-measure formulas such as the US Navy method are typically within 3 to 4 points. A 4-point error at 160 lb moves lean mass by about 6.4 lb, so compare readings taken with the same method under the same conditions rather than mixing sources.

Using lean mass for protein and training targets

Sports nutrition guidance commonly recommends 1.6 to 2.2 g of protein per kg of total body weight for people training hard, and some coaches scale instead to lean mass (roughly 2.2 to 3 g per kg of LBM, about 1 to 1.4 g per lb of LBM) so that heavier individuals with more body fat are not over-prescribed. Tracking lean mass during a cut is also the most direct check that the weight lost is mostly fat: if lean mass falls by more than a small fraction of total loss, the deficit is probably too aggressive or protein too low.

Worked example

Default inputs: 160 lb at 20% body fat

Fat mass:160 × 20 ÷ 100= 32.0 lb

Lean body mass:160 − 32= 128.0 lb (58.1 kg)

Protein at 1 g per lb LBM:128 × 1= about 128 g a day

If the same person drops to 150 lb at 15% body fat, lean mass is 127.5 lb: nearly all of the 10 lb lost was fat.

Tips & Best Practices

•Lean mass is the more useful number for protein targets; a common athlete range is about 1 g per lb (2.2 g per kg) of lean body mass.
•Measure body fat the same way each time, ideally in the morning before eating, so changes in lean mass reflect real change rather than method noise.
•A rising lean mass with stable weight means body composition is improving even though the scale has not moved.

Frequently Asked Questions

Is LBM the same as muscle mass?

No. Lean body mass includes bone, organs, blood, and body water as well as muscle. Skeletal muscle is typically 40 to 50% of total body weight in healthy adults, so it is a large part of lean mass but not all of it.

What is a typical lean body mass?

It depends on height, sex, and training. Because lean mass is weight minus fat, it is usually 70 to 90% of body weight: around 75 to 85% for most women and 80 to 90% for most men, higher in lean athletes and lower at higher body fat levels.

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

In everyday use they are treated as the same. Strictly, fat-free mass excludes all fat, while lean body mass includes the small amount of essential fat in cell membranes, nerves, and organs (roughly 2 to 5% of body weight in men, 10 to 13% in women). The difference does not matter for training purposes.

Can I estimate lean mass without a body fat percentage?

Yes, with height-and-weight formulas such as Boer or James, but they assume an average body composition and can be far off for muscular or very lean people. This calculator deliberately uses a measured body fat figure instead.