FFMI Calculator
Work out your fat-free mass index (FFMI), normalised FFMI, lean mass and fat mass from your height, weight and body fat percentage.
Reviewed by Dany, RightSums team · Updated
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health · Daily life · UK & US
Enter your height, weight and body fat percentage in metric or imperial units. The calculator works out your lean (fat-free) mass and fat mass, then your fat-free mass index: lean mass in kg divided by height in metres squared. It also gives a normalised FFMI, which adds 6.1 × (1.8 − height in m) so people of different heights can be compared, as Kouri and colleagues did in 1995. A table shows FFMI figures from published studies, such as a median of 18.9 for young men and 15.4 for young women. Your result is only as accurate as your body fat figure. It is an estimate and not medical advice.
Accepted inputs
- Sex
- Height (cm, or feet and inches)
- Weight (kg, stone and pounds, or pounds)
- Body fat percentage
Outputs
- Fat-free mass index (FFMI)
- Normalised FFMI (height-adjusted to 1.8 m)
- Lean (fat-free) mass and fat mass
- Fat mass index
- FFMI figures from published studies to compare with
How to use the FFMI Calculator
- Enter your sex, height, weight and body fat percentage in metric or imperial units.
- The calculator multiplies your weight by your body fat percentage to get fat mass, and the rest is your lean mass.
- It divides lean mass in kg by your height in metres squared to give FFMI, then adds 6.1 × (1.8 − height) to give normalised FFMI.
- Your result is set beside FFMI figures from published studies, with notes on what those studies did and did not show.
Frequently asked questions
How do you calculate FFMI?
Work out lean mass as weight × (1 − body fat % ÷ 100), then divide it by height in metres squared. At 80 kg, 1.80 m and 15% body fat, lean mass is 68 kg and FFMI is 68 ÷ 3.24 = 21.0. At 1.80 m the normalised FFMI is the same, because the height correction is zero.
What is normalised FFMI?
It adjusts FFMI to what it would be for someone 1.8 m tall, by adding 6.1 × (1.8 − your height in metres). At 5 ft 9 in, 170 lb and 15% body fat, FFMI is 21.3 and normalised FFMI is 21.6. Kouri's 1995 abstract prints the constant as 6.3, but later studies describe it as 6.1.
What is a normal FFMI?
In a study of 5,635 healthy Swiss adults, the median FFMI at ages 18 to 34 was 18.9 for men and 15.4 for women (Schutz et al. 2002). A woman of 1.65 m, 62 kg and 28% body fat has an FFMI of 16.4. These are averages from one population, not targets.
Is an FFMI of 25 the natural limit?
Not a firm one. Kouri et al. (1995) found that 74 male athletes who had not used steroids reached a normalised FFMI of up to 25.0, and called the findings preliminary. Later, 26.4% of 235 US college football players were above 25 (Trexler et al. 2017). A result over 25 does not prove steroid use.
How accurate is an FFMI calculator?
It is only as good as your body fat figure. At 80 kg and 1.80 m, each 1 point of body fat shifts lean mass by 0.8 kg and FFMI by about 0.25, so a tape estimate that is 4 points out moves FFMI by about 1. A DXA scan gives a more reliable body fat figure than tape or home methods.
Sources
The rates and rules in this tool come from:
- NHS: Calculate your body mass index (BMI) for adults
- NHS: Overweight and obesity in adults
- NHS inform: Obesity
- NHS: Malnutrition
- NHS: Calculate body mass index (BMI) for children and teenagers
- NIH: Checking your browser - reCAPTCHA
- NIH: Fat-Free Mass Index in NCAA Division I and II Collegiate American Football Players - PMC
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