Fat-Free Mass Index CalculatorFree online fitness & health calculator — instant results, no sign-up
Calculate FFMI and its height-normalized value from measured fat-free mass.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
Sign in to save results and favorites.
About the Fat-Free Mass Index Calculator
The Fat-Free Mass Index Calculator uses measured fat-free mass and height to calculate FFMI, a height-adjusted measure of non-fat body mass. It also reports FFMI normalized to a reference height of 1.80 m using an approximate height correction. This tool requires fat-free mass directly; it does not estimate it from body weight or body-fat percentage.
- Measured fat-free mass (kg)
- Your measured body mass excluding fat, including muscle, bone, organs, and body water, entered in kilograms (default: 60 kg).
- Height (cm)
- Your standing height entered in centimeters (default: 175 cm).
Formula and method
h = H / 100; FFMI = M / h²; FFMI_normalized = FFMI + 6.1 × (1.80 − h). With M = 60 kg and H = 175 cm: FFMI = 60 / 1.75² = 19.59 kg/m²; FFMI_normalized = (60 / 1.75²) + 6.1 × (1.80 − 1.75) = 19.9 kg/m².
- MMeasured fat-free mass in kilograms.
- HHeight entered in centimeters.
- hHeight converted to meters.
- FFMIFat-free mass divided by height squared, in kg/m².
- FFMI_normalizedFFMI adjusted to the reference height of 1.80 m, in kg/m².
- 6.1Empirical height-correction coefficient, expressed in kg/m³ when height is in meters.
- 1.80Reference height in meters used for normalization.
Convert height from centimeters to meters, then divide measured fat-free mass by height in meters squared. Add 6.1 times the difference between 1.80 m and the entered height to obtain normalized FFMI. Keep full precision during calculation, then display FFMI to two decimal places and normalized FFMI to one decimal place.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Measured fat-free mass60 kg
- Height175 cm
Results
- FFMI19.59 kg/m²
- Normalized to 1.80 m19.9 kg/m²
- NoteApproximation; individual results vary.
How to use the Fat-Free Mass Index Calculator
- 1Obtain a fat-free mass measurement in kilograms; do not substitute total body weight or skeletal muscle mass.
- 2Enter that value in Measured fat-free mass (kg), which defaults to 60.
- 3Enter your standing height in Height (cm), which defaults to 175; height must be greater than zero.
- 4Run the calculation to view FFMI and the value normalized to 1.80 m.
- 5Read both results alongside the approximation note, and use consistent measurement methods when tracking changes.
Reading your result
The FFMI row reports fat-free mass relative to height squared: the default inputs produce 19.59 kg/m². The Normalized to 1.80 m row applies the height correction and displays 19.9 kg/m²; it is an adjusted index, not a prediction of your body composition at a different height. The Note row states “Approximation; individual results vary.” Higher FFMI means more fat-free mass relative to height squared, but does not by itself establish better health, strength, or fitness.
Limitations
Results depend on the accuracy of the fat-free mass measurement and height entry. Body-composition methods can disagree, and hydration or measurement conditions can affect estimated fat-free mass. Fat-free mass includes more than skeletal muscle, so FFMI is not a direct muscle-mass measure. The height-normalization equation is an empirical approximation rather than a universal biological correction and may be less appropriate for children or people at height extremes. The calculator does not account for age, sex, or training history and cannot diagnose health conditions or determine performance-enhancing drug use.
Common questions
Can I enter body weight instead of measured fat-free mass?+
No. Body weight includes fat, while this calculator requires mass excluding fat. Using total body weight would overstate FFMI; skeletal muscle mass alone would omit other fat-free tissues.
Why is normalized FFMI higher than FFMI with the default inputs?+
The default height of 175 cm is below the 1.80 m reference height, so the formula adds a positive correction. With 60 kg of fat-free mass, FFMI is 19.59 kg/m² and the normalized result is 19.9 kg/m² after rounding.
What happens to the height correction above or at 1.80 m?+
Above 1.80 m, the correction is negative, so normalized FFMI is lower than unadjusted FFMI. At exactly 1.80 m, the correction is zero and the two values are equal before display rounding.
Does an increase in FFMI prove that I gained muscle?+
No. At a fixed height, an increase indicates more measured fat-free mass, but changes in body water or measurement error can also contribute. Compare measurements taken with the same method under similar conditions.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
You might also like
BMI Calculator
Body mass index with category, healthy weight range, BMI Prime and Ponderal Index.
Calorie Calculator
Daily calories to maintain, lose or gain weight.
Body Fat Calculator
Estimate body fat using the U.S. Navy tape method.
BMR Calculator
Basal metabolic rate with Mifflin-St Jeor and Harris-Benedict.
Ideal Weight Calculator
Ideal weight from four well-known formulas.
Pace Calculator
Running pace, speed and finish time.
Results are estimates for informational purposes and are not financial, medical or legal advice.