Body Fat and Fat Free Mass Index (FFMI)

The calculator calculates the body fat percentage using the Navy method and the YMCA method. The methods calculate a rough estimate of the body fat percentage and the second part calculates the fat free mass index (ffmi).

Calculator for body fat part

Neck size
Waist size
Hip size

Body fat percentage according to Navy and YMCA method

Here, a body fat content may be indicated when e.g. from a body fat measurement a more accurate value than the calculated one is known. By default, the calculated body fat percentage is used after the Navy method.

Body fat %

Fat Free Mass Index (FFMI) and Fat Free Mass (FFM)

The FFMI is an index that goes beyond the simple BMI. The BMI does not consider how the weight comes about, whether through muscle or fat. The FFMI is more meaningful here, as it takes into account the body fat percentage. A high FFMI signals a good state of training ie a high amount of muscle. The upper limit for the FFMI is 25 for men and 22 for women. Thus one can read off the potential that can be achieved through training and nutrition in one's own FFMI. Men should aim for a FFMI over 20 and women over 17.


The diagram shows the FFMI curve in relation to weight and body fat percentage. The star in the diagram indicates the currently calculated FFMI value.

Body fat table women





very high

20 to 39

under 21%

21% to 33%

33% to 39%

above 39%

40 to 59

under 23%

23% to 34%

34% to 40%

above 40%

60 to 79

under 24%

24% to 36%

36% to 42%

above 42%

Body fat table men





very high

20 to 39

under 8%

8% to 20%

20% to 25%

above 25%

40 to 59

under 11%

11% to 22%

22% to 28%

above 28%

60 to 79

under 13%

13% to 25%

25% to 30%

above 30%

Formulas for the calculation of the body fat percentage

Body fat (Navy, Woman) = 163.205⋅log(waist + hip - neck) - 97.648⋅log(height) - 104.912

Body fat (YMCA, Woman) = (74.11⋅waist - 3482) / weight -8.2

Body fat (Navy, Man) = 86.010⋅log(waist - neck) - 70.041⋅log(height) - 30.30

Body fat (YMCA, Man) = (74.11⋅waist - 4464) / weight -8.2

Units are cm and kg

Formulas for the calculation of FFM and FFMI

FFM = weight⋅(100 - Body fat percentage) / 100

FFMI = FFM / height2 + 6.3⋅(1.8 - height)

Units are Body fat in percent, height in m and weight in kg


Neck size

Wrap the measuring tape around the neck, beginning at about one inch from the meeting of your neck and shoulders. This may also coincide with the bottom part of your Adam's apple. Come fully around the neck, leaving no dangling space in between the neck and the tape. Don't pull too tightly so as to create unnecessary tension, just enough so that you are getting a true measurement. Make sure the tape is level and not being held at an angle.


Waist size

Find the top of your hip bone and the bottom of your ribs. Breathe out normally. Place the tape measure midway between these points and wrap it around your waist.

Hip size

Your natural waist is the smallest part of your torso, where your body dips in. Your hips are below that, and they are usually wider than your waist. Your hip measurement includes your butt and your hips. Your hip measurements should be taken at where your hips are the widest. That's because when you're taking measurements, you're trying to get an accurate representation of your body, and the hips represent the widest point on your bottom half.

Body Mass Calculators

Here is a list of calculators with which it is easy to calculate the corresponding body indices:

Calculation of the Body Indices Calculator for the Body Indices BSI Calculator BMI Calculator AMI Calculator Broca Calculator Ponderal Calculator Body fat and FFMI WHtR Calculator WHR Calculator

Body Mass Tables

BMI Tables BMI Index