FFMI Calculator (Fat-Free Mass Index)

FFMI Calculator (Fat-Free Mass Index)

This FFMI calculator is for calculating your body’s Fat-Free Mass Index. This approach is more exact than the BMI (Body Mass Index) and overcomes its limitations when working with well-trained individuals, such as professional athletes. The article below explains what FFMI is, compares BMI to FFMI, and describes the FFMI scale, which allows you to categorize your results.

You’ll need to know your body fat percentage to do a good calculation. If you don’t know what this parameter is, use the body fat calculator to find out. Check out our alternate calculation techniques in the army body fat calculator and US body fat calculator if you’re looking for more body fat measurements.

FFMI – Fat-Free Mass Index

Fat-Free Mass Index is abbreviated as FFMI. It describes how much muscle mass you have in relation to your height and weight. FFMI, like the well-known and comparable BMI, belongs to the family of body indexes. Although the FFMI is not as widely used as the BMI, it is more exact and offers information on a person’s condition and health.

The Fat-Free Mass Index calculates muscle mass based on three factors:

  • 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).


The BMI (Body Mass Index) is a measurement based on your weight and height. The findings are categorized according to established norms, allowing you to determine if your weight is optimum, normal, overweight, or obese.
However, there are several drawbacks to this approach, the most notable of which is that it ignores the weight of your lean muscle mass and your body fat percentage.

Although it may not appear to be a major issue at first look, BMI’s opponents are correct. Two persons of various heights and weights, for example, can have the same BMI while having different proportions of fat and muscle.

Why is FFMI better than BMI?

When a person accumulates weight as a result of an increase in fat tissue, it indicates that the individual has become less healthy. It is beneficial for an athlete (or fitness enthusiast) to gain weight as a result of increased muscular mass. From the standpoint of BMI, both circumstances are the same: a rise in weight leads to an increase in BMI index. The Fat-Free Mass Index is here to help with a solution.

FFMI is defined in a way that permits fat increase and muscle gain to be distinguished. The FFMI index decreases as fat mass grow, while the FFMI index rises as muscle mass increases. This discrepancy allows FFMI to accurately assess a person’s physique and health state.

Fat-Free Mass scale

FFMI rangeDescription
below 18Below average
18 – 20Average
20 – 22Above average
22 – 23Excellent
23 – 26Superior
26 – 28Suspicion of steroid use
more than 28Steroid usage likely

Note that:

  • scores of FFMI between 26-27.9 may indicate usage of steroids, but still might be attainable naturally,
  • scores of FFMI between 28-30 are highly unlikely to be achieved naturally without steroid usage.

How to calculate FFMI?

  • 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].

FFMI calculator – how to use it properly

Create an example calculation to help you learn how to use the FFMI calculator properly. Assume that the calculation is based on Steve, a guy with a height of 180 cm, a weight of 75 kg, and a body fat percentage of 22%. It goes like this if you follow the steps:

irst, 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?

Apply the following formula:
Weight [kg] * (1 – (body fat [percent]/ 100) Equals fat-free mass

Because weight is measured in kilograms, the outcome, FFMI, is likewise measured in kilograms.

What is a healthy fat mass index?

The average FFMI for a man is 18-20, and for a woman, 14-17. However, in athletes, the result may be greater (and still healthy!) whereas, in skinnier persons, it may be lower.

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?

All of our bodily components that did not have fat when we were born are considered fat-free mass:

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