Free FFMI Calculator
Use this free FFMI Calculator to estimate your Fat-Free Mass Index from height, weight, body fat percentage, and sex. It helps you understand how much lean mass you carry relative to your height.
Enter your details below and click the button to calculate your FFMI instantly.
How to Use This FFMI Calculator
Select your sex, then enter your height in centimeters, weight in kilograms, and body fat percentage. Click the calculate button to get your estimated FFMI, fat-free mass, and a simple interpretation.
This tool is useful when you want more detail than BMI alone. Because FFMI focuses on fat-free mass, it can give a clearer picture of lean size relative to height.
What Is FFMI?
FFMI stands for Fat-Free Mass Index. It measures your fat-free mass in relation to your height. Fat-free mass includes muscle, bone, water, organs, and other non-fat tissues.
Unlike BMI, which uses total body weight, FFMI looks specifically at lean mass. That makes it helpful for fitness tracking, body composition reviews, and general nutrition screening.
Why Use Our FFMI Calculator?
- Estimates fat-free mass and FFMI instantly
- Uses simple inputs most people already know
- More body-composition focused than BMI alone
- Includes built-in validation for safer use
- Works smoothly on mobile and desktop
How Does This FFMI Calculator Work?
The calculator first estimates fat-free mass by subtracting fat mass from total body weight. It then divides fat-free mass in kilograms by height in meters squared.
The result is your FFMI score. The page also shows your estimated fat-free mass and a note based on a low-FFMI screening threshold.
FFMI Formula
The calculator uses these formulas:
Fat-Free Mass (kg) = Weight × (1 − Body Fat % ÷ 100)
FFMI = Fat-Free Mass (kg) ÷ Height² (m²)
Example: if your weight is 80 kg, body fat is 15%, and height is 1.80 m, your fat-free mass is 68 kg and your FFMI is 68 ÷ 3.24 = 20.99.
FFMI Interpretation Guide
FFMI does not have one universal consumer grading scale for every goal, age group, and device. However, low FFMI thresholds are commonly used in clinical nutrition screening.
Female: below 15
FFMI Example Calculation
Example: A male is 175 cm tall, weighs 78 kg, and has 18% body fat.
Step 1: Fat-Free Mass = 78 × (1 − 0.18) = 63.96 kg
Step 2: Height in meters = 1.75
Step 3: FFMI = 63.96 ÷ (1.75 × 1.75) = 20.88
This result is above the common low FFMI screening threshold for men.
Why FFMI Matters
FFMI can help you look beyond body weight alone. Two people can have the same BMI but very different body composition. One person may carry more fat-free mass, while the other may carry less.
That is why FFMI can be useful for fitness planning, lean-mass tracking, and nutrition review. Still, your result should be treated as an estimate, especially if your body fat percentage comes from a home device or visual estimate.