Example 1
- Mass: 80 kg
- Height: 180 cm
- Body fat: 15%
FFMI 21.0
80 kg, 180 cm, and 15% gives FFM 68.0 kg and FFMI 21.0, BMI 24.7.
FFMI Calculator
Enter weight, height and body-fat percent. The calculator computes FFMI (fat-free mass index): it subtracts fat, divides the rest by metres squared, and also shows the height-normalized value to 1.80 m. At 80 kg, 180 cm and 15%, FFMI is 21.0 with 68 kg fat-free.
Result
Enter weight, height, and body-fat percent. FFMI and the normalized value appear here.
FFMI = FFM / m². You enter body-fat percent yourself. A girth estimate is on the US Navy body fat page. BMI keeps the whole mass and does not subtract fat.
How it works
FFM68 kg
m²3.24
FFMI21.0
FFMI starts from fat-free mass: kilograms times (1 minus body-fat percent over 100). Then you divide that mass by height in meters squared. Eighty kilograms, 180 cm, and 15% yields 68.0 kg fat-free and FFMI 21.0. BMI at the same weight and height is 24.7 because total mass stays in the numerator.
Normalized FFMI adds 6.1 × (1.80 − height in meters). At exactly 180 cm the adjust is zero. At 170 cm a raw FFMI of 20.2 becomes about 20.8 — a fairer compare across heights.
Sex, age, and activity stay in options: a rough band plus a Mifflin and TDEE estimate from total mass. You still enter body-fat percent yourself; Navy estimates it from circumferences on a separate page.
Article hook: two athletes share a raw FFMI of 22, but one is 1.70 m and the other 1.90 m — after normalizing to 1.80 m the numbers diverge. Run both values before comparing “who has more muscle for height”. Still arithmetic from your BF%, not a steroid verdict.
Formula
FFM = kg × (1 − BF% / 100)
FFMI = FFM / m²
Normalized FFMI = FFMI + 6.1 × (1.80 − m)
BF clipped to 0–95%. Fat-Free Mass Index (Kouri et al.) plus height adjust. Body-fat % must come from another method.
How to use
- Type mass, height, and body-fat percent. Get the percent from Navy, a skinfold, a scale with electrodes, or DXA. This calculator does not guess it.
- Add sex if you want an orientation band. Age and activity add a TDEE estimate from the whole mass.
- Click Calculate. At 80 kg, 180 cm, and 15% you will see 68.0 kg FFM and FFMI 21.0, with BMI 24.7 beside them.
- Compare 60 kg, 165 cm, and 25%: FFMI drops to 16.5, because the numerator is 45 kg, not the full sixty.
- The 17-22 band in men and 14-19.5 in women is rough. It depends on the percent you entered, and that percent can be off.
FFM and FFMI after subtracting fat
Lean mass first, then divide by meters squared. 80 kg, 180 cm, and 15% body fat is 68 kg FFM and FFMI 21.0.
- FFM
- Fat-free mass: kg × (1 − BF% / 100). At 80 kg and 15% that is 68 kg. Body-fat percent must come from another method; this calculator does not invent it.
- FFMI
- Fat-Free Mass Index: FFM / m². 68 / 1.80² = 21.0. Not BMI from total weight; 80 kg at 180 cm without subtracting fat would be a different ratio.
- BF%
- The body-fat percent field, clamped to 0-95%. At 15% of 80 kg you keep 68 kg lean, and only that remainder goes into FFMI.
Examples
Example 2
- Mass: 60 kg
- Height: 165 cm
- Body fat: 25%
FFMI 16.5
60 kg, 165 cm, and 25% gives FFM 45.0 kg and FFMI 16.5, BMI 22.0.
Example 3
- Mass: 90 kg
- Height: 185 cm
- Body fat: 18%
FFMI 21.6
90 kg, 185 cm, and 18% gives FFM 73.8 kg and FFMI 21.6, BMI 26.3.
Example 4
- Mass: 70 kg
- Height: 175 cm
- Body fat: 20%
FFMI 18.3
70 kg, 175 cm, and 20% gives FFM 56.0 kg and FFMI 18.3, BMI 22.9.
Example 5
- Mass: 85 kg
- Height: 178 cm
- Body fat: 12%
FFMI 23.6
85 kg, 178 cm, and 12% gives FFM 74.8 kg and FFMI 23.6, BMI 26.8.
Example 6
- Mass: 55 kg
- Height: 160 cm
- Body fat: 28%
FFMI 15.5
55 kg, 160 cm, and 28% gives FFM 39.6 kg and FFMI 15.5, BMI 21.5.
Example 7
- Mass: 95 kg
- Height: 190 cm
- Body fat: 16%
FFMI 22.1
95 kg, 190 cm, and 16% gives FFM 79.8 kg and FFMI 22.1, BMI 26.3.
Example 8
- Mass: 75 kg
- Height: 170 cm
- Body fat: 22%
FFMI 20.2
75 kg, 170 cm, and 22% gives FFM 58.5 kg and FFMI 20.2, BMI 26.0.
FAQ
What does fat-free mass index mean here?
FFMI is fat-free mass in kilograms divided by height in meters squared. You enter weight, height, and body-fat percent; the calculator does not invent the fat percent for you.
What is FFMI?
FFMI is the fat-free mass index: FFM divided by height in meters squared. At 80 kg, 180 cm and 15% body fat, FFM is 68 kg and FFMI is 21.0. It is not BMI and not a DXA scan.
How are FFMI and the normalized value counted?
FFM = kg × (1 − BF%/100), FFMI = FFM / m². Normalized = FFMI + 6.1 × (1.80 − height_m). At 80 kg, 180 cm and 15% both figures are 21.0.
Does the calculator guess body-fat percent?
No. BF% is a field you enter. A circumference estimate lives on the Navy method page. A bad percent ruins FFMI even with a good scale weight.
How does FFMI differ from BMI?
BMI divides total mass by m². FFMI divides mass after subtracting fat. At 80 kg, 180 cm and 15%, BMI is 24.7 and FFMI is 21.0. The full BMI calculator is separate.
Why normalize to 1.80 m?
Raw FFMI favors taller people. The 6.1 × (1.80 − m) correction lets you compare different heights in the same model.
What are the male FFMI bands?
Approximate: under 17; 17–18.5; 18.5–20; 20–22; 22–25; above 25. Teaching estimate only — not a diagnosis and not a DXA scan.
What are the female FFMI bands?
Approximate: under 14; 14–15.5; 15.5–17; 17–18.5; 18.5–20; above 20. Bands need sex chosen in the options.
Why age and activity?
Optionally they compute BMR (Mifflin–St Jeor) and TDEE. FFMI and fat-free mass alone do not need those fields.
Is the result muscle mass?
No. Fat-free mass includes bone, water and organs. FFMI is that mass indexed to height.
Knowledge sources
FFMI is fat-free mass over m². You enter body-fat percent yourself.
Page updated October 29, 2026.