Health Tools

Lean Body Mass Calculator

Estimate lean body mass and fat mass from body weight and body fat percentage.

Updated April 11, 2026
Free online tool
Planning and research use

Why this page exists

Lean body mass can give a more useful body-composition reference than scale weight alone when a body fat estimate is already available. This calculator helps visitors estimate lean body mass and fat mass from body weight and body fat percentage using a straightforward body-composition calculation.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Lean body mass calculator

Estimate lean body mass and fat mass from body weight and body fat percentage.

Result

140.0 lb

Estimated lean body mass based on total body weight and the body fat percentage entered.

Estimated lean body mass140.0 lb

Estimated fat mass35.0 lb

Lean body mass in kilograms63.5 kg

Body fat percentage used20.0%

Lean body mass is estimated by subtracting body fat from total body weight, so 20.0% body fat leaves about 140.0 lb of lean mass.
The remaining estimated fat mass is about 35.0 lb.
Because this calculation depends on body fat percentage, the quality of that body fat estimate affects the lean-mass result too.

This is a body-composition estimate, not medical advice. The result depends on how accurate the body fat percentage estimate is to begin with.

Planning note

Last updated April 11, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Choose a measurement system and enter body weight plus body fat percentage.

The calculator subtracts the fat-mass share from total body weight to estimate lean body mass.

It also shows the estimated fat mass for context.

Understanding your result

The result is only as good as the body fat percentage going into it. That means the lean-mass estimate is often most useful when paired with a repeatable body fat method and used as a broad planning number instead of a precise clinical reading.

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Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Add context to a body fat estimate

Use this when you already have a body fat percentage and want to understand what it means in terms of lean mass and fat mass.

Track body-composition changes over time

When body fat estimates are taken consistently, lean mass can become another way to spot broad trends.

Pair with protein planning

Some people like seeing lean-mass context alongside body fat, BMI, and protein targets when building a simple wellness plan.

FAQ

Common questions

How is lean body mass calculated here?

It is total body weight multiplied by the non-fat portion of the body, which is 100% minus the body fat percentage entered.

Why show fat mass too?

Because lean body mass is easier to interpret when you can also see the estimated amount of body weight attributed to fat mass.

Is this a medical measurement?

No. It is only an estimate built from weight and body fat percentage, not a clinical body-composition assessment.

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Health ToolsUpdated April 11, 2026