# RFM Calculator (Relative Fat Mass)

URL: https://speedycalculator.com/calculators/health/relative-fat-mass/
Last updated: 2026-10-25

> The relative fat mass calculator estimates body fat percentage from just height and waist circumference. RFM was developed in 2018 and correlates with DEXA-measured body fat better than BMI.

## Inputs

- Sex
- Height (cm, m, mm, in, ft)
- Waist circumference (cm, m, mm, in, ft)

## Results

- Relative fat mass

## Formula

```
RFM = 64 − 20 × (height ÷ waist) + 12 × sex   (sex = 1 for women, 0 for men)
```

## Explanation

RFM needs only a tape measure, making it a quick alternative to BMI for estimating body fat.

### How to use the RFM Calculator

- **Sex**
- **Height**
- **Waist circumference**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Divide height by waist circumference, apply the formula and add 12 for women.

### Inputs explained

FieldWhat to enterSexChoose one: Male, FemaleHeightUnits: cm, m, mm, in, ftWaist circumferenceUnits: cm, m, mm, in, ft
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Sex: Male; Height: 175 cm; Waist circumference: 88 cm.

Results — **Relative fat mass = 24.2 % body fat**.

## FAQ

**Where should I measure the waist?**
At the level of the belly button, standing.

**How accurate is RFM?**
Studies found it classified obesity more accurately than BMI, but it is still an estimate.

**What formula does the RFM Calculator use?**
RFM = 64 − 20 × (height ÷ waist) + 12 × sex   (sex = 1 for women, 0 for men).


## Sources

- [Woolcott OO, Bergman RN. Relative fat mass (RFM) as a new estimator of whole-body fat percentage. Sci Rep, 2018](https://www.nature.com/articles/s41598-018-29362-1)