How is RFM different from BMI?

BMI uses only height and weight and cannot distinguish muscle from fat. RFM adds a waist measurement, which captures fat distribution that weight alone misses, and directly estimates a body fat percentage rather than a weight category.

The original validation study found RFM correlated more closely with DEXA-measured body fat than BMI did, across a large, diverse NHANES sample. Like any two-measurement estimate, it is a screening tool, not a replacement for a direct body-composition scan.

Where do I measure my waist for this calculator?

Measure around your bare abdomen at the level of your navel, standing relaxed, without pulling the tape tight. Measuring at a different point or under tension will skew the result.

RFM Calculator

Relative Fat Mass (RFM) estimates body fat percentage from just two measurements — height and waist circumference. It was developed as a simpler, more accurate alternative to BMI, and validated against DEXA scans in a large NHANES sample.

Calculate your RFM

Enter metric measurements. Runs entirely in your browser.

The RFM formula

Men: RFM = 64 − (20 × height ÷ waist)

Women: RFM = 76 − (20 × height ÷ waist)

Height and waist must be in the same unit. The result is a body fat percentage estimate, clamped to a physiologically possible 2–75% range.

Body fat reference bands

Body fat percentage bands by sex
Sex	Body fat %	Band
Male	0–6%	Essential fat
Male	6–14%	Athletic
Male	14–18%	Fitness
Male	18–25%	Average
Male	25+%	Above average
Female	0–14%	Essential fat
Female	14–21%	Athletic
Female	21–25%	Fitness
Female	25–32%	Average
Female	32+%	Above average

How to use RFM

RFM is a screening estimate from two measurements, not a direct measure of body fat. Waist measurement technique matters: measuring at a different landmark, over clothing, or while pulling the tape tight will shift the result. Treat it as a general wellness reference and a useful way to track change over time under consistent measurement conditions, not as a clinical diagnosis.

Common questions

What is Relative Fat Mass?: Relative Fat Mass (RFM) is a body fat percentage estimate that uses only height and waist circumference. It was developed as a simpler, more accurate alternative to BMI for estimating body fat, and was validated against DEXA scans in NHANES survey data.
How is RFM different from BMI?: BMI uses only height and weight and cannot distinguish muscle from fat. RFM adds a waist measurement, which captures fat distribution that weight alone misses, and directly estimates a body fat percentage rather than a weight category.
How accurate is RFM?: The original validation study found RFM correlated more closely with DEXA-measured body fat than BMI did, across a large, diverse NHANES sample. Like any two-measurement estimate, it is a screening tool, not a replacement for a direct body-composition scan.
Where do I measure my waist for this calculator?: Measure around your bare abdomen at the level of your navel, standing relaxed, without pulling the tape tight. Measuring at a different point or under tension will skew the result.