Calculator · FFMI Calculator
Calculate your FFMI: What is my Fat-Free Mass Index?
The FFMI calculator relates your fat-free body mass to your height. It can help you compare body composition more consistently, but does not replace a precise medical body analysis.
Result
- Fat-free mass (FFM)
- 68.0kg
- FFMI
- 21.0
- Normalized FFMI
- 21.0
Weight × (1 − body fat).
FFM / height².
Adjusted to 1.80 m height — the comparable figure.
FFMI is a calculated metric based on estimated fat-free mass. Do not use it to diagnose health, training quality or drug use.
Method
How the calculation works
From bodyweight and body-fat percentage we compute your fat-free mass (FFM = weight × (1 − bf%/100)). FFMI is FFM divided by your height squared.
The normalized FFMI additionally corrects for height (reference 1.80 m) so values become directly comparable between shorter and taller people.
Methodology: formulas, assumptions and estimate confidence →
Estimate confidence
How reliable is this estimate?
Medium
FFMI arithmetic is unambiguous, but practical accuracy depends entirely on the body-fat input and on the suitability of the height normalization.
Interpretation
How to read your result
FFMI mathematically describes fat-free mass relative to height. The value depends directly on the body-fat percentage you enter and inherits its measurement or estimation error.
At most, use FFMI as a repeated descriptive metric under similar measurement conditions. It is not a judgment of training quality or a measure of health, strength or aesthetics.
Limits
Where this calculator ends
Fat-free mass is not measured directly; it is derived from bodyweight and body-fat percentage. Error in body fat transfers directly into FFMI and normalized FFMI.
FFMI cannot reliably determine whether a person uses performance-enhancing drugs. The frequently quoted value around 25 comes from a limited historical study and is not a biological diagnostic threshold.
Common mistakes
Common mistakes
- 01Using FFMI as a natural-status or drug-use test.
- 02Assuming the body-fat input is error-free.
- 03Reading FFMI as a health or aesthetic score.
- 04Interpreting small changes while switching body-fat methods.
- 05Treating the historical ~25 discussion as a hard biological boundary.
Example
A worked example
Illustrative calculation: 180 cm, 80 kg, estimated 15 % body fat
Estimated fat-free mass ≈ 68 kg and FFMI ≈ 21.0. Change the entered body-fat percentage and FFMI changes too, even if bodyweight and actual muscularity have not changed.
FAQ
Frequently asked questions
- What does FFMI measure?
- It calculates fat-free mass relative to height. Fat-free mass itself is estimated from the body-fat percentage you enter.
- Is FFMI a more accurate BMI?
- It answers a different question because it uses estimated fat-free mass. In exchange it inherits body-fat estimation error and is not automatically a better health metric.
- Can FFMI tell whether someone is natural?
- No. A single FFMI is not a reliable diagnosis of drug use. The popular ~25 boundary is a historical heuristic, not a biological ceiling.
- How much does the body-fat value affect the result?
- Directly. If body fat is underestimated, fat-free mass and therefore FFMI are mathematically overestimated.
- What is a good FFMI?
- This calculator deliberately does not define a universally 'good' value. It is a descriptive metric and should not be used as a health, worth or aesthetic judgment.
Sources
Sources
More
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