Enter your gender, height, and waist circumference to estimate your Relative Fat Mass (RFM) — a body fat percentage that's more accurate than BMI. The RFM Calculator applies the Woolcott & Bergman formula and returns your estimated body fat % along with a fat level classification (underfat, healthy, overfat, or obese).
Relative Fat Mass (RFM)
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Fat Level Classification
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Estimated Lean Mass
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Obesity Threshold (RFM)
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Relative Fat Mass (RFM) is a simple body fat percentage estimation formula developed by Woolcott and Bergman in 2018. It uses only two measurements — height and waist circumference — to estimate total body fat percentage. Studies show it is more accurate than BMI at identifying obesity and correlates well with DEXA scan results.
RFM uses different formulas for men and women. For adult males: RFM = 64 − 20 × (Height ÷ Waist circumference). For adult females: RFM = 76 − 20 × (Height ÷ Waist circumference). Both height and waist circumference must be in the same units (e.g., both in centimeters or both in inches).
BMI only uses height and weight, which means it cannot distinguish between fat mass and muscle mass — a muscular athlete may be classified as 'obese' by BMI. RFM uses waist circumference, which more directly reflects visceral fat and body composition. Research shows RFM better predicts body fat percentage as measured by gold-standard DEXA scans.
Healthy body fat ranges differ by sex. For men, a healthy range is roughly 8–20%, with obesity defined at 30% or above. For women, a healthy range is approximately 21–33%, with obesity defined at 40% or above. These thresholds were established by Woolcott and Bergman in a 2020 validation study.
Measure your waist circumference at the level of your navel (belly button). Stand upright and relaxed, wrap a tape measure around your bare abdomen at navel height, and take the measurement after a normal exhale. Avoid pulling the tape too tight or too loose.
A high RFM indicates excess body fat, which is associated with increased risk of type 2 diabetes, cardiovascular disease, hypertension, sleep apnea, and certain cancers. Woolcott and Bergman's 2020 study linked RFM values above the obesity cut-offs (30% for men, 40% for women) with higher all-cause mortality risk.
Reducing body fat mass typically involves a combination of a calorie-controlled, nutritious diet and regular physical activity — particularly a mix of aerobic exercise and resistance training. Losing visceral fat around the waist is especially beneficial. Consulting a physician or registered dietitian before making major lifestyle changes is recommended.
RFM is a validated screening tool but has limitations. It was developed and validated primarily in adult populations and may be less accurate for children, elderly individuals, or highly muscular athletes. It is a population-level estimation, not a medical diagnosis — for precise body composition analysis, consult a healthcare professional for DEXA scanning or hydrostatic weighing.