One estimate, three body-fat scenarios
Calculate Fat-Free Mass, FFMI and Normalized FFMI
Enter height, weight, and an estimated body-fat percentage. The calculator reports the central estimate and repeats the calculation at four percentage points below and above the body-fat input.
Fat-Free Mass Index Calculator
Enter Your Measurements
Use a current body weight and a body-fat estimate obtained under repeatable conditions. All fields are required.
Your body-composition estimate
FFMI Results
FFMI
Fat-free mass divided by height squaredNormalized FFMI
FFMI adjusted to the 1.80 m comparison heightHeight:
Weight:
Estimated body fat:
Body-Fat Sensitivity Range
The low and high scenarios change only the body-fat estimate. Height and scale weight stay fixed.
| Scenario | Body Fat | Fat-Free Mass | FFMI | Normalized FFMI |
|---|
FFMI is a body-composition estimate, not a diagnosis. No single FFMI value proves steroid use, establishes a personal natural limit, or determines health status.
The complete calculation is visible
How the FFMI Calculation Works
Every calculation uses kilograms and metres internally. Imperial values are converted before the formulas are applied.
| Output | Formula | Purpose |
|---|---|---|
| Fat-free mass | Weight × (1 − body-fat percentage ÷ 100) | Estimates total body mass that is not fat mass |
| FFMI | Fat-free mass in kg ÷ height in metres squared | Expresses estimated fat-free mass relative to height |
| Normalized FFMI | FFMI + 6.3 × (1.80 − height in metres) | Applies the original height correction to a 1.80 m comparison height |
| Sensitivity range | Repeat all three formulas at body fat −4 and +4 percentage points | Shows how body-fat estimation error changes the output |
A transparent worked calculation
Worked FFMI Example
At 175 cm, 80 kg, and an estimated 15% body fat, fat-free mass is 68.0 kg, FFMI is 22.2, and normalized FFMI is 22.5. Moving the body-fat estimate from 11% to 19% changes normalized FFMI from 23.6 to 21.5.
Keep the result inside its limits
What FFMI Can and Cannot Tell You
FFMI can provide consistent height-adjusted context for an estimated fat-free mass. Its usefulness depends on the quality and repeatability of the measurements entered.
Fat-Free Mass Is Not Muscle Alone
Fat-free mass includes muscle, bone, organs, water, and other non-fat tissue. FFMI must not be described as a direct measurement of skeletal muscle.
Body-Fat Error Changes FFMI
An underestimated body-fat percentage raises calculated fat-free mass and FFMI. An overestimated percentage lowers both values.
No Threshold Proves Drug Use
A single FFMI threshold cannot prove steroid use, determine an individual natural limit, or diagnose a medical condition.
Improve the input and apply the result carefully
Use FFMI With Body-Fat and Nutrition Context
The body-fat estimate drives the fat-free mass calculation. Use a repeatable measurement method and keep the result connected to practical nutrition decisions.
Body Fat Calculator
Estimate body fat from standardized circumference measurements and review the method's practical uncertainty.
Open the Body Fat CalculatorNutrition Guide
Set calories, protein, carbohydrate, fat, hydration, and progress checks around a realistic goal.
Open the Nutrition Guide