About the FFMI Calculator
The fat-free mass index, FFMI, is like BMI but it ignores fat. It divides your fat-free mass (muscle, bone, organs and water) by your height squared. Lifters and coaches use it to see how much muscle someone carries for their height. This calculator needs your weight, your height and an estimate of body fat, and it gives the fat-free mass, the index, the normalised index and a rating. Type your weight, your height and your body fat percentage and the fat-free mass index appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the FFMI Calculator
- 1Enter your weight, your height and your body fat percentage.
- 2Pick the units or options from the menus if the fat-free mass index tool offers them.
- 3Read the fat-free mass index in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the fat-free mass index
Strength athletes use FFMI to track progress that is not hidden by fat gain, and to set realistic goals. Researchers have used the index to estimate the natural limit of muscle mass.
The normalised value adjusts for height, since taller people carry more lean mass for the same index. It lets you compare people of different heights. Values around 25 are considered close to the upper end of what most people reach without drugs.
How the fat-free mass index is worked out
Fat-free mass = weight × (1 − body fat). FFMI = fat-free mass in kg ÷ height in metres². Normalised FFMI = FFMI + 6.1 × (1.8 − height in metres). A person who weighs 80 kg, is 180 cm tall and has 15 percent body fat has 68 kg of fat-free mass. FFMI is 68 ÷ 3.24 = 20.99, rated above average. For someone 190 cm tall and 90 kg at 12 percent fat, the normalised FFMI is 21.3.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Weight and height in two units
- Normalised value
- Fat-free mass shown
Mistakes to avoid with fat-free mass index
The result is only as good as your body fat estimate, and body fat measurements vary by method by several percentage points. The rating bands are rough guides, built from data on men; women typically have lower values. It is not medical advice.
On phone and computer
On a phone, type into the boxes one after another and read the fat-free mass index underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the fat-free mass index move. The ffmi calculator works the same on both. Compare with Body Fat Calculator and Lean Body Mass Calculator, check BMI Calculator for the usual measure, and use Protein Calculator to plan food.
Features
- Body fat estimate drives the result
- Ratings are rough
- Use one method over time
- Clear messages when the fat-free mass index inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate fat-free mass index?
Fat-free mass = weight × (1 − body fat). FFMI = fat-free mass in kg ÷ height in metres². Normalised FFMI = FFMI + 6.1 × (1.8 − height in metres). A person who weighs 80 kg, is 180 cm tall and has 15 percent body fat has 68 kg of fat-free mass. FFMI is 68 ÷ 3.24 = 20.99, rated above average. For someone 190 cm tall and 90 kg at 12 percent fat, the normalised FFMI is 21.3.
What is the formula for fat-free mass index?
Fat-free mass = weight × (1 − body fat). FFMI = fat-free mass in kg ÷ height in metres². Normalised FFMI = FFMI + 6.1 × (1.8 − height in metres). The ffmi calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is a good FFMI?
For men, 18 to 20 is average, 20 to 22 above average, and 22 to 25 is high. The tool shows where you sit.
Why normalise for height?
Because the plain index rises with height. The correction lets taller and shorter people be compared.
How accurate is the body fat figure?
Skinfold calipers, scales and scans can differ by several percentage points. Use the same method each time to track changes.
Is this ffmi calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.