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Body Fat Calculator
Estimate body fat percentage with the US Navy tape-measure method, plus fat mass, lean mass and your ACE category.
FFMI Calculator
Calculate fat-free mass index (FFMI) and height-normalized FFMI from height, weight and body fat percentage.
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How to use this calculator
Enter your values after choosing the type of calculation in the tabs. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.
Formula
fat-free mass = weight (kg) × (1 − body fat %)
FFMI = fat-free mass ÷ height (m)²
normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
The normalization, from Kouri et al. (1995), adjusts to a reference height of 1.8 m because taller people naturally have a slightly lower FFMI.
Interpreting FFMI
In the study by Kouri, Pope, Katz & Oliva (1995), men who had never used anabolic steroids averaged a normalized FFMI near 20, and the highest values among them were around 25. Many readers use 25 as a rough ceiling for drug-free muscularity, but it isn’t a hard limit, and body-fat error moves the number a lot.
| Normalized FFMI | Rough description (men) |
|---|---|
| under 18 | Below average |
| 18–20 | Average |
| 20–22 | Above average |
| 22–25 | Very muscular |
| 25 + | Uncommon without drugs |
Why FFMI instead of BMI?
BMI can’t tell muscle from fat, so lifters often register as “overweight”. FFMI removes fat mass first, which makes it a better gauge of muscle relative to height.
Frequently asked questions
What is a good FFMI?
For men, about 20 is average and 22+ is very muscular. Values for women run about 3–4 points lower.
Is an FFMI of 25 the natural limit?
It was roughly the top of the drug-free group in a 1995 study, so it’s a useful reference, not a rule.
About this tool
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- Expert review pending
- Last updated
- 31 Oct 2026
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