Free calculator
FFMI and fat-free mass calculator
Enter your height, weight, and body-fat percentage to estimate your fat-free mass and FFMI. No account needed.
How FFMI is calculated
Fat-free mass is body weight minus estimated fat mass. FFMI divides that fat-free mass by height squared, using kilograms and metres:
Fat mass (kg) = weight (kg) × body fat (%) ÷ 100
Fat-free mass (kg) = weight (kg) − fat mass (kg)
FFMI (kg/m²) = fat-free mass (kg) ÷ height (m)²
Imperial inputs are converted before calculation: 1 lb = 0.45359237 kg; 1 in = 0.0254 m; 1 ft = 12 in. Results are rounded for display only.
What does your FFMI mean?
FFMI describes fat-free mass relative to height. It does not measure strength or genetic potential, determine steroid use, or establish a universal natural limit. There is no population ranking or target score here.
How much can you trust the estimate?
A higher body-fat input gives a lower estimate of fat-free mass and FFMI at the same height and weight. An inaccurate body-fat percentage carries through to both results. Changes in fat-free mass can also include water and other components, so a change in the estimate is not necessarily a change in muscle.