Relative Fat Mass Calculator (RFM)
Relative Fat Mass (RFM) is a body fat percentage estimator that requires only two measurements: height and waist circumference. Developed by Woolcott and Bergman in 2018 from a dataset of over 300 DEXA scans, RFM demonstrated stronger agreement with directly measured body fat than BMI and a range of other anthropometric indices. Because it incorporates waist circumference, RFM captures central adiposity in a way BMI cannot. This makes it particularly useful for identifying people with normal weight but high body fat (sometimes called metabolically obese normal weight). Enter your height and waist measurements to get your estimated body fat percentage and a classification of your body fat level.
RFM formula (Woolcott and Bergman, 2018)
Men: RFM = 64 - (20 x Height / Waist)
Women: RFM = 76 - (20 x Height / Waist)
Height and waist must be in the same unit.
Example for a man 175 cm tall with 88 cm waist: RFM = 64 - (20 x 175/88) = 64 - 39.77 = 24.23%.
Relative fat mass: frequently asked questions
What is relative fat mass (RFM)?
Relative Fat Mass is a body fat percentage estimate developed by Woolcott and Bergman (2018) using only height and waist circumference. In validation studies, RFM outperformed BMI in predicting body fat percentage measured by DEXA scan, making it a practical alternative to more complex measurements.
How is RFM calculated?
For men: RFM = 64 - (20 x Height/Waist). For women: RFM = 76 - (20 x Height/Waist). Both height and waist must be in the same unit. The result is a body fat percentage estimate.
What is a healthy body fat percentage?
Healthy body fat ranges depend on sex and age. For adult men, 10-20% is fit, 21-25% is acceptable, above 25% is overweight. For adult women, 18-28% is fit, 29-35% is acceptable, above 35% is overweight. Athletes typically have lower percentages.
How does RFM compare to BMI?
BMI does not directly measure fat - it is a weight-to-height ratio. RFM uses waist circumference, which directly reflects abdominal fat distribution. Studies show RFM better identifies individuals with excess body fat, particularly those with normal BMI but elevated body fat (a pattern known as normal-weight obesity).
What measurements do I need for RFM?
You need your standing height and your waist circumference at the midpoint between your lowest rib and the top of your hip bone, measured at the end of a normal exhale. Both must be in the same unit (both cm or both inches - this calculator handles either).
Official sources
- Woolcott OO, Bergman RN (2018). Relative Fat Mass (RFM) as a new estimator of whole-body fat percentage. Scientific Reports: PubMed: 30337705.
- Centers for Disease Control and Prevention: About Adult BMI.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.