Lean Body Mass Calculator

Estimate lean body mass from body weight and body-fat percentage. Enter your own values below to see lean body mass and check the method behind it.

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Your inputs

Change the example values to match your situation.

Your result

Let’s work it out.

Fill in your inputs and select Calculate.
Your result and breakdown will appear here.

How this calculator works

Lean mass = body weight × (1 − body-fat fraction).

Before you use the result

  • Estimates for general information. They do not diagnose a condition or replace a qualified clinician’s assessment.

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What is Lean Body Mass Calculator?

Lean Body Mass Calculator helps you estimate lean body mass from body weight and body-fat percentage.

The main result is lean body mass, with a breakdown of fat mass. The formula, example and assumptions below explain how to interpret it.

How to use Lean Body Mass Calculator

Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.

  1. Gather body weight (kg) and measured / estimated body fat (%). Use values from the same situation or reporting period.
  2. Replace the example body weight with your own value, then complete the other fields. Check the displayed units.
  3. Select Calculate and read lean body mass with its result breakdown. Change one input and calculate again to compare a second scenario. Reset restores the original example.
  • Enter body weight in kg, at least 0.001. Decimals are accepted.
  • Enter measured / estimated body fat in %, at least 0 and at most 70. Decimals are accepted.

Lean Body Mass Calculator: a worked example

With the inputs below, the result is 56 kg (lean body mass). Follow the example, then replace these illustrative values with your own.

Example inputs and output
Input or outputExample value
Body weight (kg)70 kg
Measured / estimated body fat (%)20 %
Lean body mass56 kg
Fat mass14 kg

Understanding the Lean Body Mass result

Read lean body mass alongside fat mass. These describe different parts of the same calculation.

Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.

  • Example Fat mass: 14 kg

Lean Body Mass Calculator: assumptions and common mistakes

A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.

  • Estimates for general information. They do not diagnose a condition or replace a qualified clinician’s assessment.
  • Health estimates are context-dependent. Age, pregnancy, illness, medication and individual measurements can affect interpretation; these tools do not diagnose a condition.

For wider guidance, visit World Health Organization. The formula and scope of this specific tool are stated on this page.

Lean Body Mass Calculator FAQs

What does Lean Body Mass Calculator calculate?

Lean Body Mass Calculator helps you estimate lean body mass from body weight and body-fat percentage. Its main output is lean body mass in kg.

What inputs do I need for Lean Body Mass Calculator?

You need body weight (kg) and measured / estimated body fat (%). Use the field labels and units to match your figures to the formula.

Which formula does Lean Body Mass Calculator use?

Lean mass = body weight × (1 − body-fat fraction).

What is a worked example for Lean Body Mass Calculator?

Example inputs: Body weight: 70 kg; Measured / estimated body fat: 20 %. The result is 56 kg (lean body mass).

How should I enter body weight?

Enter body weight in kg, at least 0.001. Decimals are accepted.

How do I choose measured / estimated body fat?

Enter measured / estimated body fat in %, at least 0 and at most 70. Decimals are accepted. The example uses 20 %; replace it if your circumstances differ.

How should I read lean body mass?

Read lean body mass alongside fat mass. These describe different parts of the same calculation.

Why might my Lean Body Mass Calculator result differ from my records?

Estimates for general information. They do not diagnose a condition or replace a qualified clinician’s assessment. Differences in entered values, units or rounding can also change the comparison.

Can I compare two scenarios in Lean Body Mass Calculator?

Yes. Note your first lean body mass, change body weight or another input, and select Calculate again. Editing a field clears the old result so it is not mistaken for a new calculation.

Is Lean Body Mass Calculator free, and where are my inputs calculated?

This calculator is free to use without signing in. Its formula runs in your browser; calculator inputs are not sent to a calculation API. The inputs reset to the example values when you reset the form or start a fresh page.