FFMI Calculator
Calculate fat-free mass index and the height-normalized FFMI
Fat-free mass index compares lean mass with height. Enter weight, height, and body fat percentage. The result is FFMI and a height-normalized FFMI. For body weight alone, use the BMI calculator. For a body-fat estimate from measurements, use the body fat calculator. Lean mass without the height index is on the lean body mass calculator.
Calculator Inputs
Pounds or kilograms
Inches or centimeters. 70 in is 5 ft 10 in.
Results
Enter values above to see your results
FFMI is a body-composition index, not a medical diagnosis or a statement about steroid use.
How to use this calculator
- Choose pounds and inches, or kilograms and centimeters.
- Enter weight, height, and body fat percentage.
- Read FFMI and the normalized FFMI. Sex does not change the formula. It only changes the note about the often-cited figure of 25.
How the calculation works
Fat-free mass is weight × (1 − body fat ÷ 100). FFMI is that lean mass in kilograms divided by height in meters squared.
Normalized FFMI uses the Kouri height correction: FFMI + 6.1 × (1.8 − height in meters). It adjusts the index to a height of 1.8 m. The same correction is used for every height entered here.
What the number 25 means
A normalized FFMI around 25 was an upper range reported in a study of men. It is not a diagnosis, a drug test, or a personal limit. It also comes from male subjects, so it is not a female reference range.
FFMI is not BMI
BMI uses total weight. FFMI removes the estimated fat mass first, then indexes what remains to height. Two people with the same BMI can have different FFMI values if their body fat differs.
Worked example
180 lb, 70 in, 15% body fat
180 lb and 70 in= 81.65 kg and 1.778 m81.65 × (1 − 0.15)= 69.40 kg69.40 ÷ 1.778²= 21.95FFMI + 6.1 × (1.8 − 1.778)= 22.09Tips & Best Practices
- •The result is only as good as the body-fat percentage you enter.
- •70 inches is 5 feet 10 inches. 178 centimeters is about 5 feet 10 inches.
Frequently Asked Questions
How is FFMI calculated?
Convert weight to kilograms and height to meters. Fat-free mass is weight times one minus the body-fat fraction. FFMI is fat-free mass divided by height squared.
What is normalized FFMI?
Normalized FFMI adds 6.1 × (1.8 − height in meters) so people of different heights can be compared with a 1.8 m reference.
Does sex change the FFMI formula?
No. The formula on this page is the same for men and women. The note about 25 refers to a study of men.
Guides & Articles
Due Date From Ovulation or Conception Date
Add 266 days to an ovulation date or a conception date. A worked example, why both dates use the same rule, and when the period method is the better start.
How Accurate Are Pregnancy Due Dates?
A due date is the 40-week mark from a period, or 38 weeks from ovulation. Most births are not on that exact day. What moves the estimate, and what replaces it.
How Many Days Is a Pregnancy?
280 days (40 weeks) from the last menstrual period, or 266 days (38 weeks) from conception. Same model, different starting point, plus the term labels clinicians use.