Height (cm) Enter your height in centimetres (e.g., 175)

Waist Circumference (cm) Measure around your belly button level (e.g., 85)

Sex Select sex Male Female Select your biological sex as it affects the formula used

Quick Examples:

Average Adult Male Average Adult Female

Calculate Clear

This calculator provides estimates that may vary from clinical measurements. For accurate body composition analysis, consult a healthcare professional.

What Is Relative Fat Mass

Relative Fat Mass, or RFM, is a way to guess how much body fat a person has. It uses only two things you can measure at home: your height and your waist size. Unlike some other methods, you do not need a special machine or scale. RFM was made to be a simple tool that works well for most people. It gives you a percentage number that shows your estimated body fat level.

How Relative Fat Mass Is Calculated

Formula

The formula works in three steps. First, it divides your height by your waist size to get a ratio. This ratio tells you how tall you are compared to how wide your waist is. Then, it multiplies that ratio by 20. Finally, it subtracts that number from 64 if you are male or 76 if you are female. The result is your estimated body fat percentage. A taller person with a smaller waist will get a lower number, which means less estimated body fat.

Why Relative Fat Mass Matters

Knowing your estimated body fat percentage helps you understand your overall health better than weight alone. A person who weighs the same as someone else may have very different body fat levels. RFM gives you a quick way to check where you stand.

Why Body Fat Awareness Is Important for General Health

Carrying too much body fat is generally associated with a higher chance of health problems like diabetes, heart disease, and joint pain. When you do not track your body fat, you may not notice changes that could affect your health over time. RFM offers a simple check that may help you spot trends early and discuss them with a doctor if needed.

For Males and Females

The RFM formula uses different numbers for males and females because their bodies store fat differently. Females naturally carry more body fat for biological reasons, so a female RFM of 30% is not the same as a male RFM of 30%. Always compare your result to the right reference range for your sex.

Relative Fat Mass vs Body Mass Index

Body Mass Index, or BMI, uses only your weight and height. RFM uses height and waist size instead. This small change matters because BMI cannot tell the difference between muscle and fat. A person who is very muscular may have a high BMI but low body fat. RFM is generally better at guessing true body fat because waist size is more closely tied to fat levels than total weight is.