Lean Body Mass Calculator

What is a lean body mass calculator?

A lean body mass calculator estimates the weight of everything in your body that is not fat — your muscle, bone, organs, connective tissue and the water inside them. The remainder, your fat mass, is simply your total weight minus that lean figure. The tool above uses the Boer formula, a well-known equation that needs only your sex, weight and height to return a lean body mass (LBM) value in kilograms or pounds.

Lean body mass is a more useful number than weight alone when you care about body composition. Two people at the same scale weight can carry very different amounts of muscle and fat, and knowing your lean mass helps you set protein targets, dose certain medications, judge fat loss, and track whether a diet is costing you muscle. Lean body mass is often used interchangeably with fat free mass, and that is how this calculator treats it.

How does the lean body mass calculator work?

This calculator uses the Boer formula, published by P. Boer in 1984, which estimates lean body mass directly from height and weight. The equation differs by sex:

• Men: LBM (kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2
• Women: LBM (kg) = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3

Once LBM is known, the tool derives two more figures:

• Fat mass = total weight − lean body mass
• Implied body fat % = fat mass ÷ total weight × 100

The terms are straightforward:

• weight — your total body weight in kilograms.
• height — your standing height in centimetres.
• LBM — lean body mass, the fat free portion of your weight, in kilograms.

If you enter imperial units, the tool converts before applying the formula: pounds are multiplied by 0.45359237 to get kilograms, and inches are multiplied by 2.54 to get centimetres. So a 175 lb input becomes 79.38 kg, and a 70 in input becomes 177.8 cm. The Boer coefficients are then applied to those metric values, which is why every example below is worked in kilograms and centimetres.

Examples

Here are fully worked calculations that match the tool’s output exactly.

Example 1 — Man, 80 kg, 180 cm

• LBM = 0.407 × 80 + 0.267 × 180 − 19.2
• = 32.56 + 48.06 − 19.2 = 61.42 kg lean body mass
• Fat mass = 80 − 61.42 = 18.58 kg
• Implied body fat = 18.58 ÷ 80 × 100 = about 23.2%

Example 2 — Woman, 65 kg, 165 cm

• LBM = 0.252 × 65 + 0.473 × 165 − 48.3
• = 16.38 + 78.045 − 48.3 = 46.13 kg lean body mass
• Fat mass = 65 − 46.13 = 18.87 kg
• Implied body fat = 18.87 ÷ 65 × 100 = about 29.0%

Example 3 — Man, 175 lb, 70 in (imperial)

• Convert: 175 × 0.45359237 = 79.38 kg; 70 × 2.54 = 177.8 cm
• LBM = 0.407 × 79.38 + 0.267 × 177.8 − 19.2
• = 32.31 + 47.47 − 19.2 = 60.58 kg (about 133.6 lb)
• Fat mass = 79.38 − 60.58 = 18.80 kg
• Implied body fat = 18.80 ÷ 79.38 × 100 = about 23.7%

Example 4 — Woman, 70 kg, 170 cm

• LBM = 0.252 × 70 + 0.473 × 170 − 48.3
• = 17.64 + 80.41 − 48.3 = 49.75 kg lean body mass
• Fat mass = 70 − 49.75 = 20.25 kg
• Implied body fat = 20.25 ÷ 70 × 100 = about 28.9%

Notice that height carries a large weight in the formula, especially for women (the 0.473 coefficient), which is why taller people are credited with more lean mass at the same body weight.

Boer formula reference

This table shows the exact Boer coefficients the calculator applies. Multiply your weight in kg and height in cm by the matching numbers, then subtract the constant.

Sex	Weight coefficient	Height coefficient	Constant
Men	0.407 × kg	0.267 × cm	− 19.2
Women	0.252 × kg	0.473 × cm	− 48.3

For a man at 80 kg and 180 cm this gives 32.56 + 48.06 − 19.2 = 61.42 kg, matching Example 1; for a woman at 65 kg and 165 cm it gives 16.38 + 78.045 − 48.3 = 46.13 kg, matching Example 2.

Common uses

A lean body mass estimate is useful in several everyday situations:

• Set protein targets. Many nutrition guides scale daily protein to lean mass rather than total weight, so dieters can keep muscle while losing fat.
• Track recomposition. When you lose fat and gain muscle, scale weight barely moves; watching lean mass and fat mass separately shows the real change.
• Estimate body fat. The implied body fat percentage gives a quick composition check without calipers or a scan.
• Inform dosing. Some clinical drug doses are based on lean body mass rather than total weight, which is why this number appears in medical contexts.

Tips and common mistakes

• Match your units. Enter weight and height in the same system the tool expects; the imperial path converts pounds and inches for you, so do not pre-convert and double up.
• Use standing height. Measure height without shoes, standing tall; an extra centimetre noticeably shifts the result through the height coefficient.
• Do not confuse lean mass with muscle. Lean body mass includes bone, organs and water, so it is always larger than your skeletal muscle mass.
• Re-measure under the same conditions. Weigh yourself at the same time of day to keep the trend meaningful from week to week.
• Treat the body fat figure as derived. The implied body fat percentage comes from the LBM estimate, so it inherits any error in the formula rather than measuring fat directly.

Limitations and notes

The Boer equation is a population estimate built only from height and weight, so it cannot see your actual body composition. A heavily muscled athlete and a sedentary person of identical height and weight will get the same lean body mass figure even though their real composition differs greatly. The formula is most reliable for typical adults near average builds and becomes less accurate at the extremes of height, weight or muscularity. Direct methods such as DEXA scans, hydrostatic weighing or bioelectrical impedance measure lean and fat tissue far more precisely and will not always agree with this number.

Health disclaimer: This lean body mass calculator is provided for general information and education only. It is not medical, nutritional or fitness advice, and it is not a substitute for professional assessment. Consult a qualified healthcare professional before making decisions about your health, diet or training.

For more body and fitness self-checks, try the TDEE calculator for daily calorie burn, the macro calculator to split those calories into protein, carbs and fat, and the calorie deficit calculator to plan fat loss while protecting lean mass, then browse the full fitness category for more tools.