Relative Fat Mass (RFM) Calculator
Estimate body fat percentage with the Relative Fat Mass (RFM) formula from height and waist — only a tape measure needed.
How to use this tool
- Measure your height in centimetres.
- Measure your waist at the navel after breathing out normally.
- Select your sex so the correct constant is applied.
- Read your estimated body fat percentage and category.
The Relative Fat Mass (RFM) calculator estimates your body fat percentage from just your height and waist measurement. It is a newer, tape-measure-only alternative to skinfold and BMI-based estimates.
Formula
Men: RFM = 64 − 20 × (height ÷ waist)
Women: RFM = 76 − 20 × (height ÷ waist)
Height and waist must be in the same units (the ratio is unitless), and the result is body fat as a percentage.
How it works
Relative Fat Mass (RFM) was published by Woolcott and Bergman in Scientific Reports (2018). It estimates whole-body fat percentage from the ratio of height to waist circumference plus a sex constant. In the original study it tracked DXA-measured body fat more closely than BMI for most adults, while needing only a tape measure.
Because RFM relies on a single waist measurement, technique matters. Measure at the level of the navel, standing relaxed, at the end of a normal exhalation, with the tape snug but not compressing the skin. RFM is intended for adults; it is not validated for children or during pregnancy.
This calculator is provided for general information and education only and is not medical advice. Body-shape indices are screening estimates, not diagnoses. Always consult a qualified healthcare professional before making decisions about your health.
Worked example
Man, 175 cm tall, 90 cm waist
- Height ÷ waist = 175 ÷ 90 = 1.94444
- 20 × 1.94444 = 38.8889
- Men use the constant 64: 64 − 38.8889 = 25.1111
- Round to two decimals = 25.11%
Relative Fat Mass = 25.11% (High category)
Body fat category ranges by sex (RFM %)
| Category | Men | Women |
|---|---|---|
| Essential fat | < 8% | < 14% |
| Fit / athletic | 8 – 19.9% | 14 – 24.9% |
| Average | 20 – 24.9% | 25 – 31.9% |
| High | ≥ 25% | ≥ 32% |
Key terms
- Relative Fat Mass (RFM)
- An anthropometric estimate of total body fat percentage derived from the height-to-waist ratio and a sex-specific constant.
- Waist circumference
- The distance around the abdomen, here measured at the navel; a proxy for central (visceral) fat.
- DXA
- Dual-energy X-ray absorptiometry, a clinical scan used as the reference standard against which RFM was validated.
- Essential fat
- The minimum body fat needed for normal physiological function — roughly 3-5% in men and 10-13% in women.
Frequently asked questions
- How accurate is the RFM formula?
- In the 2018 validation study, RFM estimated DXA body fat with less error than BMI for the majority of adults. It remains an estimate, not a measurement, and accuracy varies between individuals.
- Is RFM better than BMI?
- RFM directly uses waist size, so it reflects central fat that BMI ignores. Two people with the same BMI can have very different RFM values.
- Do I need to know my weight for RFM?
- No. RFM is unusual among body-fat estimates because it needs only height and waist circumference, not body weight.