RFM Calculator — Relative Fat Mass
Estimates body fat from just waist and height — no scale, no other tape points. The newest of the methods here, and the one that beats BMI at its own job.
RFM (Relative Fat Mass, Woolcott–Bergman 2018) turns your height-to-waist ratio into a body-fat estimate. Two measurements, no weighing — and because it reads your waist, where fat actually sits, it tracks fat better than BMI. WIMSTA shows it as one voice in a range.
RFM reads only your waist and height — no scale needed. Because it uses waist (where fat sits), it tracks body fat better than BMI, which sees only total weight. Two people at the same BMI but different waists get different RFM — and that's the point. It's still one estimate; the full calculator shows it inside a range with US Navy, CUN-BAE and Deurenberg.
Two measurements, better than BMI
BMI knows only your total weight, so it can't tell a heavy-but-lean build from a fatter one. RFM uses waist circumference — a direct read on where fat is stored — so two people at the same BMI with different waists get different, and more truthful, RFM values. In the original study it was more accurate than BMI vs DXA.
It's close cousin to the waist-to-height ratio: WHtR is a risk screen (the 0.5 boundary), RFM turns the same ratio into an estimated body-fat percentage.
Newer, and built on a diverse cohort
Most body-fat equations are decades old and trained on one population. RFM was derived on NHANES, n ≈ 12,000 (US, multi-ethnic) and validated against DXA — large, recent and multi-ethnic, which is why it generalises better than many older formulas.
Great for
A fast, scale-free body-fat estimate from two tape reads; a strong all-rounder across body types.
Watch for
Waist measurement is everything — measure consistently. Still an estimate, not a scan. Not for under-18s or pregnancy.
One estimate is a guess. See the range.
RFM, US Navy, CUN-BAE and Deurenberg rarely agree on the same body. The calculator shows the honest range they land in — and where it sits against the healthy zones.
Open the body-fat calculatorWoolcott & Bergman (2018). Sci Rep 8:10980. Derived on NHANES, n ≈ 12,000 (US, multi-ethnic), validated against DXA (more accurate than BMI vs DXA). Coefficients verified against the primary source and covered by our test suite.
FAQ
What is RFM (Relative Fat Mass)?
RFM estimates body-fat percentage from just your waist and height: RFM = 64 − 20 × (height ÷ waist) for men, and 76 − 20 × (height ÷ waist) for women. Published by Woolcott and Bergman in 2018, it needs no scale and no other measurements.
Is RFM better than BMI?
For estimating body fat, yes. RFM uses your waist — where fat actually sits — so it tracks fat better than BMI, which only knows total weight. In the original study, validated against DXA on a large US cohort, RFM was more accurate than BMI. It also errs less between sexes and body types.
What measurements do I need for RFM?
Only two: waist circumference and height, in the same unit. Measure the waist with a flexible tape around the narrowest point (or at the navel), relaxed, on bare skin — where you read the waist changes the result more than small real changes do.
Is RFM the same as waist-to-height ratio?
They are related — RFM is built on the height-to-waist ratio — but not the same. Waist-to-height is a risk screen with a 0.5 boundary; RFM converts the ratio into an estimated body-fat percentage. WIMSTA offers both.
How every formula is sourced: the method page.