Relative Fat Mass (RFM) Calculator

Relative Fat Mass Explained

The relative fat mass (RFM) index estimates body fat percentage based on the ratio of height and waist measurements. This fat mass index is considered a simple anthropometric procedure, easier to estimate than other body fat percentage methods and more accurate than the body mass index (BMI).

RFM has been generally validated and a recent 2020 study by the original authors has also established gender specific cut-off points for obesity.

The relative fat mass equation is gender specific:

• RFM for adult males = 64 – 20 x (Height / Waist circumference)
• RFM for adult females = 76 – 20 x (Height / Waist circumference)

For the best results, when using a tape measure and recording the height and waist circumference, the tape measure should be placed at the top of the hip bone and wrapped around the body. You can use either the Metric or the English system, whichever is more convenient, but ensure that both measurements are input in the same unit system.

Woolcott and Bergman (2020) propose RFM cut-offs of 40% for females and 30% for males to diagnose obesity and higher mortality risk.

The relative fat mass result can also be interpreted in line with the cut-offs established by the American Council on Exercise:

The relative fat mass equation was derived based on data from the National Health and Nutrition Examination Survey (NHANES) 1999–2004 (n=12,581) and validated with data from the NHANES 2005–2006 data (n = 3,456). The RFM formula was derived following analysis on some 365 anthropometric indices.

In the validation dataset, the RFM performance was compared to BMI and shown to be a better predictor of whole-body fat percentage, measured by dual energy X-ray absorptiometry (DXA), among women and men. RFM also had fewer false negative cases of body fat-defined obesity among women and men.

References

Original reference

Woolcott OO, Bergman RN. "Relative fat mass (RFM) as a new estimator of whole-body fat percentage ─ A cross-sectional study in American adult individuals". at Cedars-Sinai Medical Center. Nature Research Journal (Scientific report article number: 10980 of 2018).

Other references

Guzman-Leon AE et al. External validation of the relative fat mass (RFM) index in adults from north-west Mexico using different reference methods. PLoS ONE 2019; 14(12): e0226767.

Woolcott OO, Bergman RN. Relative Fat Mass as an estimator of whole-body fat percentage among children and adolescents: A cross-sectional study using NHANES. Sci Rep 9,15279 (2019).

Woolcott OO, Bergman RN. Defining Cutoffs to Diagnose Obesity Using the Relative Fat Mass (RFM): Association With Mortality in NHANES 1999-2014. Int J Obes (Lond) 2020;44(6):1301-1310.