FFMI Calculator
FFMI is fat-free mass divided by height squared. Normalized FFMI adjusts that index toward a 1.8 m reference height. Enter height, weight, and a body-fat percent. Informational, not a diagnosis.
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How to calculate FFMI
- Choose metric or US units for height and weight.
- Enter height, weight, and body-fat percent. Fat-free mass is weight times (1 minus body-fat fraction).
- Read FFMI as FFM in kg divided by height in meters squared.
- Read normalized FFMI, which adds 6.1 times (1.8 minus height in meters).
- Compare with lean mass and Navy tape pages when you need another body-composition view. Nothing is uploaded.
Fat-free mass index
FFM / height² with optional height normalization
| FFM | Weight × (1 - body-fat fraction) |
|---|---|
| FFMI | FFM (kg) / height (m)² |
| Normalized FFMI | FFMI + 6.1 × (1.8 - height_m) |
| Inputs | Height, weight, body-fat percent |
| Related entities | Lean mass, BMI, body-fat percent |
| Advice | Informational. Not a steroid screen or medical claim. |
What FFMI measures
Fat-free mass index puts lean tissue on a height-scaled footing, similar to how BMI scales total mass. Two people with the same BMI can show different FFMI values when body-fat percents differ. This page stays arithmetic: it does not judge natural limits or training status.
How FFMI and normalized FFMI are built
Fat-free mass equals total mass times (1 - body-fat percent / 100). FFMI equals that mass in kilograms divided by height in meters squared. Normalized FFMI adds 6.1 × (1.8 - height_m) so shorter and taller frames are nudged toward a 1.8 m reference. At exactly 1.8 m the two indexes match.
Lean mass, body fat, BMI, and related jobs
Entities here include fat-free mass, FFMI, normalized FFMI, and body-fat percent. Raw lean and fat kilograms from a typed percent live on lean body mass. A circumference body-fat estimate is on Navy body fat. Whole-body mass over height squared without fat splitting is BMI.
Use cases
Tracking lean mass density after a cut or bulk when you already trust a body-fat estimate. Comparing two training logs that list height, weight, and a scale BF%. Classroom demos that separate BMI from lean-mass indexing. Not a clinical sarcopenia tool and not a drug-test threshold.
Default numbers
At 180 cm, 80 kg, and 15% body fat, fat-free mass is 68 kg. Height squared is 3.24 m², so FFMI is about 20.99. Normalized FFMI matches FFMI at this height because the 1.8 m offset is zero.
Limits
Body-fat input quality dominates the result. Tape, BIA, and DEXA disagree. Normalized FFMI is a published adjustment, not a universal standard. Informational only. See the disclaimer. CZNull does not receive the measurements.