Relative Fat Mass (RFM) Calculator
Estimate your body-fat percentage with the Relative Fat Mass (RFM) formula from just height and waist circumference, with the ACE body-fat category for your sex.
How it works
Men: RFM = 64 − 20 × (height ÷ waist) · Women: RFM = 76 − 20 × (height ÷ waist) (height and waist in the same unit)
Relative Fat Mass was derived by Woolcott and Bergman (Scientific Reports, 2018) from NHANES data with DXA scans and estimates whole-body fat percentage better than BMI, especially in women. Because it uses a ratio, any unit works as long as height and waist are measured the same way. Categories follow the American Council on Exercise body-fat ranges.
Worked example
A man 175 cm tall with a 90 cm waist: 175 ÷ 90 = 1.94, so RFM = 64 − 20 × 1.94 = 25.1% body fat, just into the ACE Obese band for men (≥ 25%). A woman with the same measurements would read 37.1%.
Frequently asked questions
How accurate is relative fat mass?
In the original study RFM matched DXA body fat better than BMI and misclassified fewer people as obese or not. Individual error is still several percentage points, similar to tape-measure methods.
Where do I measure my waist for RFM?
At the level of the navel (umbilicus), standing, after breathing out normally, with the tape horizontal and snug.
Can I use inches?
Yes. The formula uses height divided by waist, so inches, centimetres or any unit work as long as both measurements use the same one.
What is a healthy RFM?
Using ACE categories, about 14–24% for men and 21–31% for women covers the fitness and average ranges; 25% and above for men or 32% and above for women counts as obese.
Related calculators
This calculator gives an estimate for general fitness and education only. It is not a diagnosis — results from field tests and prediction equations can differ from laboratory measurements, so talk to a doctor or qualified exercise professional before acting on them.