Fat Free Mass Index Calculator

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Definition of FFMI

Fat-Free Mass Index which takes height and weight into account and used to describe muscle mass of a person. FFMI is correlated with BMI although having some differences as well. FFMI is not used commonly as BMI but is more precise and used for particular people like Bodybuilders and athletes.

The fat-free mass index uses three factors to measure muscle mass in body which are:

  • Body Weight- measured in kilograms and pounds
  • Body height- measured in meters, inches, feet, and centimeters
  • Body fat- measured in percentage

FFMI Interpretation and Normal Values

Here is the table of scores that can be used by anyone to know where they stand regarding muscle mass and how much they can gain naturally and with the use of steroids.

The following tables classify the FFMI indexes:

For men:

Description Body fat percent FFMI range
Skinny guy 10-18 below 18
Average weighted guy 20-27 18-20
Obese guy 25-40 20-22
Athlete/ gym user    10-18 22-23
Gym freak 6-12 23-26
Heavyweight Bodybuilder/ professional athlete 8-20 26-28
Steroid user with regular gym 8-20 More than 28


  • The values between 26-27.9 show a person might be using steroids but it is possible to achieve this naturally
  • The values above 28 show person using steroids as it is not possible to achieve naturally

The above FFMI chart shows FFMI ranges for men, here is a table that shows FFMI ranges in women.

Description Body fat percent FFMI range
Skinny girl/woman 20-25 14-15
Average weighted woman 22-35 14-17
Obese woman 30-45 15-18
Athlete/ gym user 18-25 16-17
Gym freak 15-22 18-20
Heavy weight Body Builder/ professional athlete 15-30 19-22

Calculation of FFMI

There are several formulas used widely to calculate body FFMI and other related measures. Here are the formulas according to each measurement:

  • To calculate Total body fat:

Total Body Fat = Weight in Kg × (body fat % / 100)

  • Equation to measure lean weight without fat:

Lean Weight = Weight in Kg × (1 - (body fat % / 100)

  • To calculate FFMI:

FFMI = (Lean Weight in Kg / 2.2)/ ((Feet × 12.0 + Inches) × 0.0254)2

  • Here is how to calculate adjusted FFMI:

Attuned FFMI = FFMI + (6.3 × (1.8 - (Feet × 12.0 + Inches) × 0.0254))


These formulas allow you to calculate muscle mass in the human body but to save time you can use our calculator for free. Furthermore, you can freely switch between units according to your understanding and knowledge on our calculators like for height you can use cm, meter, inches and feet.

To use our calculator all you need is to follow these quick steps:

  • Fill the field first field by adding your body fat in percentage
  • Add you height in centimeter, meter, inches, and feet according to preference
  • Fill the last field by adding your weight in kg, US ton, tonne, pound, ounce
  • Click on the “calculate” button and you will get the answer in seconds

Correlation between BMI and FFMI

BMI is a prediction rule with classified norms that tells if a person is underweight, average or overweight. However, this parameter has limitations as it uses the only weight of a person and neglecting lean body mass and fat in the body.

BMI shows same results for two persons with different height and body structure just like if a person with a lot of muscles and other person with swollen belly; BMI will show same results for both as weight in both people is same and this is one reason BMI is not used for professional athletes, heavy weight lifters and others.

On the other hand, FFMI takes height and body fat into account and give out precise results showing actual muscles mass of a person.

There is a difference between gaining weight in an unhealthy way which is not a good thing and gaining muscles while doing exercise and using a proper diet. FFMI is what distinguishes between muscle gain and fat gain.

If fat in the body increases FMI decreases and vice versa. FFMI is used in the different medical field as well, as it estimates correctly health condition of a person. For persons doing exercise and achieving health goals, BMI is useless for them. FFMI is what can help them out for the regular checkup of their muscle mass. Use our calculator and FFMI according to the need while sitting in-home or anywhere else.

BMI is not totally useless it has its own advantages vary situation to situation. You can calculate your Body mass index as well by using our BMI calculator.

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