Relative Fat Mass (RFM) Calculator
Estimate your body fat percentage using the Relative Fat Mass (RFM) index — a straightforward formula based on your height and waist circumference that research shows correlates better with DEXA-measured whole-body fat than BMI.
Sex
cm
cm
Average
- 1
Height ÷ waist ratio
178 ÷ 85 = 2.0941 - 2
Ratio × 20
2.0941 × 20 = 41.8824 - 3
RFM = base − ratio × 20
64 − 41.8824 = 22.1Base constant 64 for men (76 for women).
How does this calculator work?
RFM = 64 − 20 × (height/waist) for men and 76 − 20 × (height/waist) for women, with both measurements in centimetres. Proposed by Woolcott & Bergman (2018), it predicts whole-body fat percentage from just two tape measurements and outperforms BMI against DEXA scans in validation studies.
Formula
How this is calculated
The Relative Fat Mass (RFM) index was proposed by Woolcott and Bergman in a 2018 study published in Scientific Reports. It uses two simple tape measurements — standing height and waist circumference at the navel — to predict whole-body fat percentage. In the study it outperformed BMI and several other anthropometric indices when validated against DEXA (dual-energy X-ray absorptiometry) scans in a large multi-ethnic sample.
The formula divides height by waist circumference (a proxy for central adiposity), multiplied by the constant 20. Men use a base of 64 and women a base of 76, reflecting the naturally higher fat percentage in female bodies. A narrower waist relative to height increases the ratio and lowers the RFM, while a wider waist relative to height reduces the ratio and raises the RFM.
Limitations: RFM is a population-level estimate, not a direct measurement. Very muscular individuals, pregnant women, people with unusual fat distribution, or children may get inaccurate readings. As with any body-composition estimate, interpret the result as a trend indicator rather than a precise fat percentage, and compare it with other measures over time.
Frequently asked questions
In the original Woolcott & Bergman (2018) study, RFM showed a closer correlation with DEXA-measured whole-body fat percentage than BMI, waist-to-height ratio, or body adiposity index, particularly in women. However, it remains a two-measurement approximation — expect a few percentage-point margin versus DEXA.
Measure at the navel (umbilicus) with the tape parallel to the floor and relaxed (not sucked in). Use the same measurement point each time to track trends consistently.
Approximate healthy ranges from fitness guidelines: men 14–21% (fitness to average zone), women 22–28%. Values below the essential/athletic threshold may indicate insufficient fat stores, while values in the obese range are associated with higher cardiometabolic risk.
Also known as
TG we-Calculate Editorial Team. (2026). Relative Fat Mass (RFM) Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/relative-fat-mass-calculator
TG we-Calculate Editorial Team. "Relative Fat Mass (RFM) Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/relative-fat-mass-calculator.
TG we-Calculate Editorial Team, "Relative Fat Mass (RFM) Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/relative-fat-mass-calculator
@misc{wecalculate_relative_fat_mass_calculator, title = {Relative Fat Mass (RFM) Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/relative-fat-mass-calculator}}, year = {2026}, note = {TG we-Calculate} }
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