Updated
Using FFMI calculator
Fat-free mass index = fat-free mass in kilograms / height in meters squared.
Body-fat measurement error carries into the result. The optional normalized result applies Kouri et al.'s correction of 6.3 times (1.8 - height), developed in 157 male athletes. It is not a universal natural-muscle limit, a steroid test, or a health classification.
A worked example
80 kg at 20% body fat and 1.80 m gives a fat-free mass of 64 kg and an FFMI of 19.8.
Before you use the result
Body-fat measurement error carries into the result. The optional normalized result applies Kouri et al.'s correction of 6.3 times (1.8 - height), developed in 157 male athletes. It is not a universal natural-muscle limit, a steroid test, or a health classification.
Example results for body weight (kg)
These examples use Body fat (%): 20; Height (meters): 1.8. They are reference calculations, not recommended settings.
| Body weight (kg) | FFMI (kg per square meter) |
|---|---|
| 40 | 9.9 |
| 80 | 19.8 |
| 160 | 39.5 |
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ToolOctopus. “FFMI calculator.” Updated 2026-09-29. https://tooloctopus.com/ffmi-calculator.
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