How to use the lean body mass calculator
Prepare the values for this calculation
Calculate fat-free/lean mass from body weight and an entered body-fat percentage. Use the formula below to check that it answers your question. Read the input units before transferring figures from a statement, measurement or dataset.
Enter and check each input
- Body weight (kg): enter a value at least 1. Use the unit named in the label or selected above. Do not leave this required field blank.
- Body fat (%): enter a value at least 0 and no more than 99.9. Use the unit named in the label or selected above. Do not leave this required field blank.
The input table gives a complete example. Keep units and time periods consistent across related fields.
Calculate and resolve any input error
Choose Calculate after entering the values. Changes also update the answer after a short pause. If an error appears, follow its message, correct the field and calculate again. Reset restores the example values.
Interpret the answer
Check Lean body mass first. With the unchanged example inputs, it is 64 kg. Interpret it using the formula and assumptions on this page.
Compare and keep a useful result
For a controlled comparison, keep every other example input unchanged and change Body weight (kg) from 80 to 88. The resulting Lean body mass is 70.4 kg. This illustrates the equation’s response to that input, rather than a forecast of real events.
Read the chart’s axis labels and data table. A scenario curve changes one stated input while holding the others fixed; it does not add external observations. Use Download graph to save an available chart as a PNG.
Use Copy result or Download CSV to keep the answer. Share tool shares the page address without placing your input values in the URL. Recheck inputs and assumptions before using the result for a decision.
Lean Body Mass Calculator formula
Lean mass=weight×(1−body-fat fraction).
Inputs and units
| Input | Format / range | Example |
|---|---|---|
| Body weight (kg) | minimum 1 | 80 |
| Body fat (%) | minimum 0; maximum 99.9 | 20 |
Worked example
Using the example inputs above, the lean body mass is 64 kg.
- Lean body mass
- 64 kg
Results and assumptions
Educational calculation only; do not use this result by itself to diagnose, treat, or make an urgent medical decision.
Fix an input or unexpected result
Body weight (kg) is required. Enter body weight (kg) using the format and bounds in the input table. Zero and an empty field are different: use zero only if it is allowed and represents your data.
If your answer differs from the example, choose Reset and compare every field, including selected units and options. Check percentage versus decimal entry and whether values describe the same period. Round only the final displayed answer when reproducing the formula.
If a discrepancy remains, report the calculator issue with the page address, non-sensitive example inputs, actual result, expected result and a reference for your calculation.