FFMI Calculator (Fat-Free Mass Index)

Created by Filip Derma and Łucja Zaborowska, MD, PhD candidate
Reviewed by Dominik Czernia, PhD candidate and Jack Bowater
Based on research by
Schutz Y, Kyle UU, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y International journal of obesity and related metabolic disorders (July 2002)See 2 more sources
Hull HR, Thornton J, Wang J, Pierson RN Jr, Kaleem Z, Pi-Sunyer X, Heymsfield S, Albu J, Fernandez JR, Vanitallie TB, Gallagher D. Fat-free mass index: changes and race/ethnic differences in adulthood. International Journal of Obesity (January 2011)Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids Clinical Journal of Sport Medicine (October 1995)
Last updated: Oct 01, 2022

This FFMI calculator is dedicated to estimating Fat-Free Mass Index of your body. This method is more precise in comparison to the BMI (Body Mass Index) and overcomes its shortcomings when dealing with people who are well trained, as well as professional sportsmen. In the article below you can find an explanation of what is FFMI, the comparison of BMI vs FFMI, and the FFMI scale which allows you to classify your results.

To perform a proper calculation, you need to know your body fat result in [%]. If you don't know it, use the body fat calculator to get this parameter. Also, if you are interested in more body fat measurements, check out our alternative calculation methods in the US navy body fat calculator.

FFMI - Fat-Free Mass Index

FFMI is the abbreviation of Fat-Free Mass Index. It describes the amount of your muscle mass in relation to height and weight. FFMI is part of the family of body indexes, together with well-known and similar BMI. Although the FFMI is less used, it is more precise than BMI, and also provides information about somebody's condition and health.

The Fat-Free Mass Index uses 3 inputs to provide a score of muscle mass:

  • Body height - measured in centimeters or in feet and inches,
  • Body weight - measured in kilograms or pounds,
  • Body fat - measured in percent units (use our body fat calculator to find your input value).


Body Mass Index is a parameter calculated from your weight and height. The results are classified according to the defined norms, and thanks to that you can say whether your weight is ideal, normal or if you are overweight or even obese. (see: ideal body weight calculator).
However, this method has its limitations, the most significant being that it doesn't take into account the weight of your lean muscle mass, and your amount of body fat.

Maybe, at first glance, it doesn't seem that big a problem, but the critics of BMI are justified. For example, two people with different heights and weights can have the same BMI, even though they have different amounts of both fat and muscle. Somebody with a lot of muscle mass can be classified negatively - as overweight or even obese. The BMI method is based only on weight, and therefore it doesn't take into account the difference in tissues and body type. From another point of view, an inactive person, someone who does not exercise and is in an overall unhealthy state, might get a very good BMI result.

Why is FFMI better than BMI?

When somebody gains weight, and it is caused by fat tissue increase, that means the person has become less healthy. When an athlete (or fitness enthusiast) put on weight because of an increase in muscle mass, it is a good thing. Both situations mean the same from BMI's viewpoint - weight increase results in BMI index increase. That is where the Fat-Free Mass Index comes in with a solution.

FFMI is defined in a way that allows distinguishing between fat gain and muscle gain. If the mass of fat increases, FFMI index goes down, and if the mass of muscle increases, FFMI rises. It is this difference that allows FFMI to correctly estimate somebody's body and health condition.
On the other hand, Body Mass index (BMI) is a general estimation of your health that works well for most of the population. Note, that for somebody who exercises daily or trains professionally, BMI is mostly useless. For that kind of person, with more muscle mass than the ordinary people, Fat-Free Mass Index is a much better, much more effective choice.

Fat-Free Mass scale

The following table indicates the classification of FFMI indexes.

FFMI range for men


below 18

Below average

18 - 20


20 - 22

Above average

22 - 23


23 - 26


26 - 28

Suspicion of steroid use

more than 28

Steroid usage likely

Note that:

  • scores of FFMI for men between 26-27.9 may indicate usage of steroids, but still might be attainable naturally,

  • scores of FFMI for men between 28-30 are highly unlikely to be achieved naturally without steroid usage.

FFMI range for women


below 15

Below average

15 - 17


17 - 18

Above average

18 - 19


19 - 21.5


21.5 - 25

Suspicion of steroid use

more than 25

Steroid usage likely

Note that:

  • scores of FFMI present approximate values for the general population - their application in real life may vary.

How to calculate FFMI?

The FFMI calculator uses currently approved mathematical formulas for computing the fat-free mass, FFMI as well as Normalized FFMI . The latter is dedicated for taller athletes who are bigger overall.

  • Body fat calculation bases on the simply equation: body fat = weight [kg] × (body fat [%] / 100). It is expressed in kilograms units [kg].
  • Fat free mass is estimated using the following method: fat free mass = weight [kg] × (1 - (body fat [%]/ 100)). Result is also expressed in kilograms [kg].
  • FFMI is calculated respectively: FFMI = fat free mass [kg]/ (height [m])². Expressed in kilograms per square meter [kg/m²].
  • For Normalized FFMI use the equation: normalized FFMI = FFMI [kg/m²] + 6.1 × (1.8 - height [m]). The same unit as in FFMI [kg/m²].

Fat-Free Mass Index calculator allows you to change the units which are displayed. You can switch between cm, m, kg, lb, etc., accordingly to your needs and preferences.

FFMI calculator - how to use it properly

Check out an example calculation, to help you have a crystal clear understanding of how to use the FFMI calculator correctly. Let's assume that the estimation is made on Steve - the man who has 180 cm, weighs 75 kilograms and have 22% of body fat. Following the steps, it goes like this:

First, fill in all the input data:

  1. Enter his height: 180 cm,
  2. Enter his weight: 75 kg,
  3. Enter his body fat: 22%.

Then, check out the calculation outcome based on these input data:

  1. The FFMI is 18.1 kg/m² - that number classifies our man to the average result - the message with the classification range is displayed automatically below the calculator.
  2. Normalized FFMI is equal to 18.1 kg/m² - it is identical to the non-normalized value because the man is not taller than the mean value of the population.
  3. Steve's fat-free mass equals: 58.5 kg,
  4. His total body fat weighs: 16.5 kg.


How to calculate FFMI?

Use the following equation:
Fat-free mass = Weight [kg] × (1 - (Body fat [%]/ 100))

Weight is expressed in kg, and so the result, FFMI, is also in kg.

What is a healthy fat mass index?

For a man, the average FFMI is 18-20, and for a woman, 14-17. However, the result may be higher (and still healthy!) in athletes or lower in skinnier people.

How to lower body fat without losing muscle mass?

There are a few rules to follow while trying to lose weight:

  1. Keep a healthy (but rational and balanced) diet.
  2. Do both cardio and weights. You need both to build your muscles and burn that fat.
  3. Take your time. Losing weight healthily, keeping your muscles, and staying healthy requires patience.

Which are examples of fat-free mass?

Fat-free mass is all of our body parts that originally do not contain fat:

  • Inner organs;
  • Bones;
  • Ligaments and tendons;
  • Connective tissue;
  • Muscles;
  • Blood; and
  • Nerves.

However, in the course of some diseases, such as obesity, diabetes, or high triglycerides, even these organs and tissues may become fatty.

Filip Derma and Łucja Zaborowska, MD, PhD candidate
Input data
Body fat
Normalized FFMI
Fat-free mass
Total body fat
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