Estimate Relative Fat Mass from height and waist circumference using the Woolcott–Bergman formula, with sex-specific body fat categories.
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Sex
Units
| Relative Fat Mass | 24.4% |
| Category | Average |
| Formula | 64 − 20 × (178.0 ÷ 90.0) = 24.4% |
| Category | Men (%) | Women (%) |
|---|---|---|
| Essential fat | < 6 | < 10 |
| Athletic | 6–14 | 10–21 |
| Fitness | 14–18 | 21–25 |
| Average | 18–25 | 25–32 |
| Obese | ≥ 25 | ≥ 32 |
Also in Body Metrics
Body Metrics
The Relative Fat Mass (RFM) index estimates body fat percentage from only two measurements — height and waist circumference — without requiring any skinfold calipers or body composition equipment. Enter your sex, height, and waist to see your estimated body fat percentage.
Men: RFM = 64 − 20 × (height ÷ waist). Women: RFM = 76 − 20 × (height ÷ waist). Both height and waist must be in the same unit (both cm or both inches). The formula was developed by Woolcott and Bergman (2018) and validated against DXA (dual-energy X-ray absorptiometry) body composition scans.
A larger waist-to-height ratio produces a higher RFM, reflecting that central adiposity (abdominal fat accumulation) is strongly associated with metabolic risk.
In the Woolcott and Bergman validation study, RFM showed stronger correlation with DXA-measured body fat than BMI in both sexes. BMI does not distinguish fat from muscle and gives the same value for a lean muscular individual and an overweight but low-muscle individual with identical height and weight. RFM captures the waist dimension directly, making it more sensitive to central fat accumulation.
Measure your waist at the midpoint between the bottom of your lowest rib and the top of your hip bone (iliac crest) — typically at or near the navel. Stand relaxed, breathe out normally, and measure at the end of a normal exhale without holding your breath in. Consistency in measurement location matters for tracking changes over time.
Frequently asked questions
RFM correlates well with DXA body fat in population studies, but like any two-measurement formula it has estimation error. In the original study, RFM showed r² values around 0.70–0.80 for body fat prediction, which is better than BMI but still leaves significant individual variability.
Yes — measuring your waist at the same location each time and recalculating RFM is a valid and practical way to track changes in central adiposity. Changes of 1–2 cm in waist measurement are detectable and meaningful.
Women naturally have a higher body fat percentage than men at the same waist-to-height ratio due to sex-specific fat distribution (more subcutaneous and reproductive fat). The higher constant in the female formula adjusts for this physiological difference.
Related
These related calculators come from the same leaf category, nearby sibling categories, or the same top-level topic.
Calculate Ponderal Index (mass divided by height cubed) as a height-proportionate alternative to BMI, with a category from underweight to obese.
Estimate body fat percentage with body measurements, then compare fat mass, lean mass, and a general body composition band.
Estimate body fat percentage using the US Navy circumference method — measure neck, waist, and hips to get fat mass, lean mass, and an ACE fitness category.
Check body mass index with metric or imperial units, then compare the result with standard adult BMI ranges and a height-based healthy weight estimate.
