Calculate your Relative Fat Mass from height and waist circumference. RFM estimates body fat percentage without a scale — 2018 Cedars-Sinai formula.
The Relative Fat Mass (RFM) is a body composition metric developed in 2018 by researchers at Cedars-Sinai Medical Center that estimates body fat percentage using only height and waist circumference — no scale required. Published in Scientific Reports, the RFM formula was derived from a large NHANES dataset and validated against DXA (Dual-energy X-ray Absorptiometry) scans, the gold standard for body composition measurement.
RFM uses a sex-specific linear equation: 64 − 20 × (height / waist) + 12 × sex, where sex is 0 for males and 1 for females. This elegantly simple formula outperformed BMI in estimating whole-body fat percentage in the validation cohort, with correlation coefficients of 0.85–0.87 against DXA-measured body fat.
The appeal of RFM lies in its simplicity and accuracy: it requires only a tape measure and a stadiometer (or wall-mounted height chart), making it practical for settings where body composition assessment is needed but scales or specialized equipment are unavailable.
RFM provides a direct estimate of body fat percentage, which is more health-relevant than BMI (a weight-to-height ratio that cannot distinguish fat from lean mass). The formula was specifically calibrated against DXA scans and shown to estimate body fat more accurately than BMI, body adiposity index (BAI), and several other anthropometric formulas. Because RFM requires no scale, it is ideal for community screenings, field research, and remote settings where minimizing equipment is important.
RFM = 64 − 20 × (Height / WC) + 12 × Sex Where: • Height and WC (waist circumference) are in the same units (cm or inches) • Sex = 0 for male, 1 for female Body fat classifications (ACE guidelines): Men: Essential 2–5%, Athletes 6–13%, Fitness 14–17%, Average 18–24%, Obese ≥25% Women: Essential 10–13%, Athletes 14–20%, Fitness 21–24%, Average 25–31%, Obese ≥32%
Result: RFM = 24.4%
For a male (sex = 0) with height 178 cm and waist 90 cm: RFM = 64 − 20 × (178 / 90) + 12 × 0 = 64 − 20 × 1.978 = 64 − 39.56 = 24.4%. This falls in the "Average" body fat range for men (18–24%), indicating a typical fat level without obesity.
Researchers at Cedars-Sinai led by Dr. Orison Woolcott analyzed body composition data from 12,581 adults in NHANES who had both DXA scans and anthropometric measurements. Using regression analysis, they found that the ratio of height to waist circumference, combined with a sex indicator, predicted DXA-measured whole-body fat percentage with high accuracy. The resulting formula was intentionally kept simple for practical clinical use.
In the validation cohort, RFM outperformed BMI, Body Adiposity Index (BAI), and other waist-based metrics for estimating body fat percentage. The key difference is that RFM directly targets fat percentage rather than using weight as a proxy. This means it better handles cases where high muscle mass inflates BMI without corresponding increases in body fat.
RFM is useful in obesity screening, nutrition counseling, and fitness assessment. Because it needs no special equipment, it can be deployed in community health fairs, rural clinics, and field research settings. Healthcare providers can use RFM as a quick body fat check during routine office visits, supplementing or replacing BMI when a more accurate fat estimate is desired.
RFM estimates whole-body fat percentage but does not indicate fat distribution (visceral vs. subcutaneous). It was validated in a U.S. population and may require recalibration for populations with different body proportions. The formula assumes a linear relationship between height/waist ratio and body fat, which may be less accurate at extreme values.
RFM is a 2018 formula from Cedars-Sinai that estimates body fat percentage using only height and waist circumference. It was derived from over 12,000 NHANES participants and validated against DXA scans. The formula includes a sex adjustment term, producing separate estimates for men and women.
For estimating body fat percentage, yes. RFM had a higher correlation with DXA-measured body fat (r ≈ 0.86) than BMI (r ≈ 0.72) in the original validation study. BMI cannot distinguish fat from muscle, whereas RFM's use of waist circumference better captures adiposity.
No. RFM requires only height and waist circumference, both measurable with a tape measure and height chart. This is one of its key advantages over BMI, body fat percentage calculators that require weight, or equipment-heavy methods like bioelectrical impedance or DXA.
Women naturally carry more essential body fat than men (for reproductive functions), so the formula includes a +12% adjustment for females. This ensures the estimate reflects sex-specific body composition norms rather than applying a single unisex equation.
For men, 14–24% is considered the fitness-to-average range, with below 6% being essential fat only. For women, 21–31% is the fitness-to-average range, with below 14% being essential. These ranges come from the American Council on Exercise (ACE) classifications.
The original study validated RFM in adults aged 20–79. Applying it to children or adolescents is not recommended because body proportions and fat distribution change significantly during growth. Pediatric body fat assessment should use age-specific methods.
The Navy method uses waist, neck, and (for women) hip circumference and produces a body fat estimate. RFM is simpler (only height and waist) and was calibrated against DXA in a larger sample. Both can be useful, but RFM is easier to measure and generally shows stronger correlation with DXA.
The formula itself does not include an age term. Body fat naturally increases with age, so younger and older adults with identical height and waist measurements will get the same RFM. For age-adjusted assessment, combine RFM with age-specific body fat guidelines.