Adult Relative Fat Mass (RFM) Calculator
Estimate adult whole-body fat percentage from height and waist circumference using the published Woolcott–Bergman RFM equation.
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About
Relative fat mass is an adult linear regression estimate based on standing height, waist circumference, and one explicitly selected published equation coefficient. It was developed and validated by comparison with DXA whole-body fat percentage, but it is not a direct measurement, diagnosis, or personal target. [1, 2, 3]
Formula
Interpretation
Regression estimate, not measurement
RFM is a regression estimate developed against DXA whole-body fat percentage. It is not DXA, BIA, a four-compartment model, or another direct or reference body-composition measurement. [1, 2]
Development and validation ages
Model development included ages 20–85; the original independent NHANES validation dataset included ages 20–69. Age does not enter the equation, and reported predictive performance was lower in older adults. [1]
Published equation variable
The original model encoded sex as 0 for male and 1 for female. This page requires an explicit published coefficient selection and does not infer, blend, or invent another coefficient. [1]
Waist measurement method
Measure standing, with the waist unclothed when practical, using a horizontal tape at the uppermost lateral border of the right ilium and read at the end of normal expiration. Repeated measurements should use the same site and technique. [1, 4]
External validation varies
A north-west Mexico study of 61 adults ages 20–37 reported supportive comparisons with DXA and other methods, but the sample was small. A Korean study of 18,706 adults found overall performance comparable with BMI while results differed by sex and analytical objective. Neither result establishes performance for every population. [2, 3]
No universal diagnostic cutoff
The original study used exploratory body-fat cut points to compare classification performance; it did not establish diagnostic RFM cut points. This page displays no Low, Normal, High, Obese, or target range. [1]
Worked arithmetic examples
Male coefficient, age 40, 175 cm height, 90 cm waist: 64 − 20 × 175 / 90 = 25.111... → 25.1%.
Female coefficient, the same measurements: 76 − 20 × 175 / 90 = 37.111... → 37.1%.
US-equivalent example: 5 ft 8.8976 in and 35.4331 in waist represent the same measurements to the shown input precision and produce the same one-decimal male result; full exact inch conversions preserve the same unrounded result.
These examples show arithmetic only, not a normal or abnormal category. The 12-percentage-point difference comes from the published equation variable; it is not a measurement-error estimate and does not prove that either coefficient applies to a particular user. [1, 5]
References
- 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. Scientific Reports. 2018;8:10980. PMID 30030479. PMCID PMC6054651. doi:10.1038/s41598-018-29362-1.
- Guzmán-León AE, et al. External validation of the relative fat mass index in adults from north-west Mexico using different reference methods. PLOS ONE. 2019;14(12):e0226767. doi:10.1371/journal.pone.0226767.
- Paek JK, Kim J, Kim K, Lee SY. Usefulness of relative fat mass in estimating body adiposity in Korean adults. Endocrine Journal. 2019;66(8):723–729. PMID 31142689. doi:10.1507/endocrj.EJ19-0064.
- CDC/NCHS. National Health and Nutrition Examination Survey: 2021 Anthropometry Procedures Manual. May 2021.
- National Institute of Standards and Technology. NIST Guide to the SI, Appendix B.8: inch to centimeter conversion.
FAQ
Relative fat mass is an adult anthropometric regression estimate of whole-body fat percentage from height, waist circumference, and a published equation coefficient.
Sources: [1]
It reproduces Woolcott–Bergman 2018: 64 − 20 × height/waist for the published male coefficient, or 76 − 20 × height/waist for the published female coefficient.
Sources: [1]
The original RFM equation uses only height and waist circumference. Weight and BMI are not inputs to this model.
Sources: [1]
They are the two historical coefficients published with the equation. The page requires an explicit selection; it does not infer a coefficient or invent a third or mixed coefficient.
Sources: [1]
This page accepts ages 20–85, the original model-development range. The original independent NHANES validation dataset included ages 20–69. Age validates the page range but does not enter the calculation.
Sources: [1]
No universal diagnostic RFM cutoff is displayed. The original research used exploratory body-fat cut points to compare classification performance; it did not establish RFM diagnostic thresholds.
Sources: [1]
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WHR
Calculate adult waist-to-hip ratio from standardized waist and hip circumferences in metric or US units.
Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.