FFMI Calculator (Fat-Free Mass Index)

Calculate your FFMI using your height, weight, and body fat percentage.

What is Fat Free Mass Index

Fat-free mass index, or FFMI, is one way to estimate lean muscle mass. Instead of measuring body mass in relation to height, like BMI, it measures the amount of lean muscle mass (or fat-free mass) relative to a person’s height.

The purpose of FFMI is to interpret body composition regardless of height.^[1] It is used to identify individuals with malnutrition, or a relatively high muscle mass.^[2]

The Importance of Body Composition

There are several different metrics used to determine overall health. One of the most easily used is body weight in relation to height.

Weight and height can be used to calculate body mass index (BMI), which is one marker of overall health. People that are obese or overweight typically have more health issues than leaner individuals.

However, body composition is just as much, if not more important than simply using BMI. Body composition takes into account your percentage of body fat and lean muscle mass instead of simply just using weight as a surrogate marker of health.

For example, higher levels of body fat have a stronger association with heart disease risk when compared to BMI.^[3]

In addition, a study from European Heart Journal found that individuals with normal weight but a high amount of body fat still had a high prevalence of metabolic syndrome and cardiovascular risk factors.^[4]

Furthermore, athletes or bodybuilders have higher muscle mass. This can place them inappropriately in an overweight or obese category based on weight or BMI alone.

Research has found that BMI alone cannot provide important information about the contribution of fat-free mass or fat mass to body weight.^[1]

This illustrates how higher percentages of lean muscle mass and lower amounts of body fat play a crucial role in health. This is where the fat-free mass index comes into play.

How to Calculate FFMI

In order to calculate fat-free mass index, you first need to know your body fat percentage.

Body fat percentage can be measured in a clinical setting using machines such as a DEXA scan, BodPod, or bioelectrical impedance scale.

If you don’t have access to these machines, you can use a body fat formula to estimate total body fat. These formulas use different body measurements, such as skinfold thickness, or use body mass index to estimate body fat percentage.

FFMI Formulas

Once you have determined your body fat percentage, you can then calculate your body fat in either kilograms or pounds.

body fat = weight [kilograms] × body fat % / 100

body fat = weight [pounds] × body fat % / 100

This number is how many pounds (or kilograms) of fat your body is carrying.

Fat-free mass is then equal to:

fat-free mass = total weight – body fat weight

These equations are sometimes combined and may be written as:

fat-free mass = weight × (1 – body fat % / 100)

This number can then be used along with height and weight to calculate FFMI using the following equation:

FFMI = fat-free mass [kilograms] / height² [meters]

As you can see, this is the same equation used for body mass index, however it substitutes weight with fat-free mass.

If you are using imperial units, the equation is:

FFMI = fat-free mass [pounds] ÷ 2.2 / (height [inches] × 0.0254)²

This equation simply uses a factor of 2.2 to convert pounds to kilograms and 0.0254 to convert inches to meters

The adjusted, or normalized, FFMI is used for individuals that are taller than the average height.

adjusted FFMI = FFMI + (6.1 × (1.8 – height [meters])

Imperial Units:

adjusted FFMI = FFMI + (6.3 × (1.8 – (height [inches]) × 0.0254))

FFMI Ranges

Once you have calculated your fat-free mass index, you can then see how this compares to a range of FFMI values.

There are no set standards for fat-free mass index ranges and the current understanding of what a normal or healthy FFMI range is limited.^[2] However, below are the ranges that one study found to be acceptable.^[1]

It is important to note, the study does not set an upper limit for FFMI because high levels do not result in negative health effects.^[1]

Normal Range for Men

table showing the normal fat-free mass index range for men

Fat-Free Mass Index	Body Fat Percentage
17-20 kg/m²	13-22%

Normal Range for Women

table showing the normal fat-free mass index range for women

Fat-Free Mass Index	Body Fat Percentage
15-17 kg/m²	25-33%

Differences Between Fat Mass in Men and Women

On average, women have lower muscle mass compared to men. Therefore they will have a lower fat-free mass index that corresponds to a similar category.

Due to their biology and physiology, men have less body fat, more muscle mass, and greater bone density compared to women.^[5] Women need higher levels of essential body fat for normal physiologic functions and childbearing.

In addition, genetics and hormone levels will also impact body fat percentage. On average, women have 6 to 11 percent more body fat than men.^[5] This accounts for the somewhat lower percentage of lean muscle mass.

Higher FFMI values indicate a higher muscle mass percent, which is often the goal for many athletes and those involved in strength training.

While scores between 26-28 may still be attainable, this may indicate usage of steroids. And FFMI values above 28 are highly unlikely to be achieved naturally without steroid usage.^[6]