Body measurements Health Calculators

Fat-Free Mass Index (FFMI)

FFMI Calculator (Fat-Free Mass Index)

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.

FFMI is an alternative to body mass index which accounts for a person’s muscle mass. The average male scores about 19 and it is hard to score above 25 without using steroids or other banned substances.

FFMI is conceptually similar to Body Mass Index (BMI). But instead of measuring body mass in relation to height, it measures the amount of muscles (fat-free mass) relative to a person’s height.

This indicator accounts for the amount of total lean muscle mass in the body. Research also suggests it can predict how much muscle your body can potentially gain.

It’s a useful indicator for people who are trying to lose weight, specifically those engaging in strength training to develop muscles and reduce body fat. FFMI is especially handy for serious body building enthusiasts.

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.

The standard FFMI levels for men and women

FFMI Ranges for Men

Description FFMI Range Body fat percent
Skinny guy 17-18 10-18
Typical average guy 18-20 20-27
Fat guy 19-21 25-40
Athlete / regular gym user 20-21 10-18
Advanced gym freak 22-23 6-12
Elite strength athlete (bodybuilders, etc.) 24-25 8-20

FFMI Ranges for Women

Description FFMI Range Body fat percent
Skinny woman 14-15 20-25
Typical average woman 14-17 22-35
Fat woman 15-18 30-45
Athlete / regular gym user 16-17 18-25
Advanced gym freak 18-20 15-22
Elite strength athlete (bodybuilders, etc.) 19-22 15-30


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. 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.


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