By Zencalcy Editorial TeamLast reviewed About us
Relative Fat Mass (RFM) estimates body fat percentage from height and waist circumference alone. It was proposed as a simpler alternative to BMI and to methods that need multiple skinfolds. It performs well in validation studies but remains an estimate.
Estimate body fat percentage from height and waist.
Men: RFM = 64 − 20 × (height ÷ waist) Women: RFM = 76 − 20 × (height ÷ waist) Height and waist in the same unit.
Woolcott and Bergman (2018) developed RFM from NHANES data. It estimates body fat percentage directly, but it cannot distinguish fat distribution or lean mass, and accuracy falls at very high body-fat levels.
| Symbol | Meaning |
|---|---|
| RFM | Estimated body fat percentage. |
| height | Standing height. |
| waist | Waist circumference in the same unit as height. |
Height ÷ waist = 175 ÷ 85 = 2.059. RFM = 64 − 20 × 2.059 = 64 − 41.2 = 22.8%. For a woman with the same measurements, RFM = 76 − 41.2 = 34.8%.
RFM was built on a straightforward observation: waist circumference carries a lot of information about body fat, and height scales it. By fitting the relationship to a large national dataset, the authors produced an equation that needs only a tape and a height. That simplicity is its strength in clinics and field research. Its limitation is that waist circumference is not a pure fat measure. It includes abdominal muscle, bone and organ volume, and it changes with bloating and posture. A very muscular person with a thick waist can get a higher RFM than their measured body fat. A person with a small waist but fat stored on the hips and thighs can get a lower value. For most people, though, the number tracks DEXA reasonably well and is far more informative than weight alone. Use it as a trend and combine it with waist-to-height ratio.
Continue with the ABSI Calculator (A Body Shape Index), Adjusted Body Weight Calculator, or the BAI Calculator (Body Adiposity Index) — or browse more body measurements tools and all health calculators.
Also see the Body Fat Calculator.
Validation studies report good agreement with DEXA at the population level, often better than BMI. Individual error remains, especially in very muscular or very lean people.
Every result is a screening estimate from published anthropometric equations, not a diagnosis or a measurement of body composition. Tape measurements should be taken snugly against the skin without compressing it, at the landmarks named in each tool. Equations were derived in specific populations and can be less accurate for athletes, older adults, children, pregnant people and people with significant oedema.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026