RFM Calculator
Body fat from two measurements — height and waist, nothing else.
Measurements
Estimated body fat
Two measurements, and why that is the point
Relative Fat Mass was published by Woolcott and Bergman in 2018 and needs only height and waist:64 − 20 × (height ÷ waist) for men, with 76 in place of 64 for women. No weight, no neck, no hip, no callipers. It was derived against DEXA across a large NHANES sample and validated to predict body fat more accurately than BMI, particularly for women.
The simplicity is the argument for it. Every additional measurement is another chance to introduce error, and waist is the single circumference most strongly tied to the fat that matters metabolically. The Navy method needs three or four measurements; RFM needs two, and gets comparable or better agreement with DEXA.
Where it struggles is the same place every circumference method struggles. It cannot distinguish visceral from subcutaneous fat, it reads high for very muscular people whose waist carries muscle rather than fat, and it inherits whatever inconsistency is in your tape technique. Measure at the midpoint between the lowest rib and the top of the hip bone, at the end of a normal exhale, and measure the same way every time — the trend matters more than any single figure.
Medical disclaimer. This calculator is for general information and education only. It is not medical advice, not a diagnosis, and not a substitute for professional care. RFM is a population-derived estimate rather than a measurement, and it reads inaccurately for very muscular individuals and during pregnancy.Speak to a doctor or another qualified clinician about any health decision.Last reviewed .
Frequently asked questions
What is Relative Fat Mass?
A body fat estimate published in 2018 that uses only height and waist circumference. The formula is 64 − 20 × (height ÷ waist) for men and 76 − 20 × (height ÷ waist) for women, derived against DEXA scans in a large population sample.
Is RFM more accurate than BMI?
For estimating body fat percentage, yes — that was the point of developing it. BMI cannot distinguish fat from muscle at all, while RFM uses waist circumference, which tracks body fat far more closely. It was found particularly more accurate than BMI for women.
How does RFM compare to the Navy method?
Comparably accurate with fewer measurements. Navy needs neck and waist for men, plus hips for women; RFM needs only height and waist. Fewer measurements means fewer opportunities for tape error.
Where do I measure my waist for RFM?
At the midpoint between the bottom of your lowest rib and the top of your hip bone, which is usually just above the navel. Measure at the end of a normal breath out, with the tape horizontal and snug but not compressing.
Why does RFM read high for muscular people?
Because it interprets waist girth as fat. A muscular midsection adds circumference without adding fat, so the estimate overshoots. This affects every circumference-based method, not just RFM.