Lean Body Mass Calculator (LBM)

What this calculator estimates

Separate an entered body weight into estimated fat mass and lean mass using the body-fat percentage you supply. This is a direct calculation, not a new measurement of body fat.

Inputs and calculation method

Enter kilograms and body-fat percentage. The tool subtracts estimated fat mass from weight, and also displays a fixed protein comparison of 2 grams per kilogram of calculated lean mass.

Formula and units

Lean mass (kg) = body weight × (1 − body fat % ÷ 100). Fat mass = body weight − lean mass. The protein comparison is lean mass × 2 g, rounded to a whole gram; it is a preset illustration rather than an independently assessed requirement.

How to use it

1. Enter body weight in kg.
2. Enter body fat as a percentage, such as 28 rather than 0.28.
3. Calculate and read the fat and lean components together.
4. Keep the body-fat measurement method consistent when comparing results.

Worked example

At 70 kg and 28% body fat, fat mass is 70 × 0.28 = 19.6 kg and lean mass is 50.4 kg. The fixed protein comparison is 50.4 × 2 = 100.8 g, displayed as 101 g.

How to read the result

Lean mass includes muscle, water, bone and organs. It should not be read as kilograms of muscle. The protein comparison uses lean mass, whereas the separate protein calculator uses total body weight and goal presets.

Common mistakes

• Entering a fraction instead of a percentage.
• Assuming every change in lean mass is muscle gain or loss.
• Comparing body-fat estimates from different devices as if their methods were identical.

Method limitations

The arithmetic inherits all error in the body-fat estimate. The fixed protein comparison does not account for overall diet, training or medical nutrition requirements.

Supporting guides

• What Is Lean Body Mass? A Practical Body Composition GuideLean body mass explained clearly: what it includes, how to estimate it, and why it matters for protein, strength, fat loss and scale-weight interpretation.
• Lean Body Mass vs Body Fat: What Each Number Tells YouCompare lean body mass and body-fat percentage so weight loss, muscle gain and body recomposition are judged with better context.
• How To Estimate Lean Body Mass Without Overtrusting The NumberA practical guide to estimating lean body mass using body weight, body-fat percentage, measurements and trend checks.
• Lean Body Mass And Protein Targets: How To Connect The NumbersUse lean body mass to set more sensible protein targets during fat loss, maintenance and strength training.
• Lean Body Mass For Strength Training: What To Track Beyond Scale WeightHow strength training changes the way you should read lean body mass, body weight, waist measurements and performance.
• Why Scale Weight Hides Body Composition ChangesScale weight is easy to measure but poor at explaining fat loss, muscle gain and water shifts. Here is how to read it with lean body mass.

Using the estimate

Use the result to understand the arithmetic behind an existing body-fat estimate. Check the input’s uncertainty before interpreting small lean-mass changes.