This RFM calculator (or Relative Fat Mass calculator) predicts body fat mass using only two body measurements - height and waist circumference. This estimation is more accurate than the well-known body mass index (BMI), which often misclassifies obesity.

Do you want to know how to calculate your fat mass? Check the article below to find out more about the relative fat mass index! ⬇️

Body fat mass - an essential part of the human body

Body fat (in other words adipose tissue) is an essential component of the human body. Its primary function is energy storage, but it also has other vital functions, such as protecting internal organs and producing hormones (e.g., leptin). The percentage of body fat in people generally varies according to age and sex. Women usually have a greater body fat percentage than men (due to reproductive and hormonal functions), and older people tend to have a higher body fat percentage.

While a certain amount of body fat is essential for human health, excessive adipose tissue is not good for human health either. Research shows that a high body fat percentage is associated with morbidity and mortality; therefore, the state of excessive accumulation of body fat is classified as a disease - obesity. This condition is an important risk factor of many other disorders, such as cardiovascular disease, type 2 diabetes, and some forms of cancer.

How to calculate your fat mass?

Nowadays, there are quite a lot of methods available to measure body fat mass. They include very sophisticated measurements, such as underwater weighing and whole-body air displacement plethysmography, or the more popular ones - dual-energy X-ray absorptiometry (DEXA) and bioelectrical impedance analysis (BIA).

Unfortunately, all of those techniques require specialist equipment, and they are not always available (or cheap!). Therefore, different mathematical formulas were created to calculate fat mass. Check the paragraph below to see which equation we have used in our RFM calculator.

If you are interested, you can compare your results with other calculators that estimate body composition:

Relative fat mass index and relative fat mass chart

Our RFM calculator estimates body fat mass percentage using equations developed in 2018 by researchers from Sports Spectacular Diabetes and Obesity Wellness and Research Center (Cedars-Sinai Medical Center, USA). The formula is different for men and women, and it uses only two measurements: a person's height and their waist circumference.

The equations look as follows:

  • MEN:

RFM = 64 - (20 * height / WC)

  • WOMEN:

RFM = 76 - (20 * height /WC)


RFM - relative fat mass index, expressed in %;

height - expressed in cm; and

WC - waist circumference, expressed in cm.

This equation is based on the height-to-waist ratio, and is more accurate than BMI when used to estimate body fat mass. You can find the interpretation of the results in the relative fat mass chart below:

Fat level men (%)
Fat level women (%)
Extremely low level of fat
Essential fat
2 - 5
10 - 13
6 - 13
14 - 20
14 - 17
21 - 24
18 - 24
25 - 31

RFM calculator - a practical example

Let's use a practical example to show you how to calculate your fat mass. We will calculate the relative fat mass of Kathy, who is 170 cm tall and has a waist circumference of 72 cm. Don't worry if you are using inches - the relative fat mass calculator will convert them into centimeters for you.

  1. We will be using the relative fat mass equation for females:

RFM = 76 - (20 * height / WC)

  1. Fill in the necessary information. After doing so, the equation will look like this:

RFM = 76 - (20 * 170 / 72)

  1. We're almost there! There is just an easy calculation left.

RFM = 76 - (20 * 2.36)

RFM = 76 - 47.2

RFM = 28.8

  1. Kathy's relative fat mass is equal to 28.8 %. According to the relative fat mass chart displayed in the RFM calculator, this is an average result. Well done Kathy!
Joanna Michałowska, PhD candidate