Estimate adult body-fat percentage with the published Relative Fat Mass (RFM) equation using height and waist. Metric or imperial, private and browser-local.
01 / ADULT MEASUREMENTS
RFM is the simple default: height and hip-bone waist. Weight is optional, for the mass breakdown only.
02 / ESTIMATE & BREAKDOWN
Enter the measurements required by your chosen method to estimate body fat.
03 / MEASUREMENT GUIDE & CONTEXT
The published sex parameters are model coefficients, not a gender-identity assessment. All methods are estimates with population and measurement limitations, not diagnoses or direct measurements. Pregnancy and medical circumstances can make them unsuitable. No ideal target, weight-loss prescription or amount of fat to lose is calculated.
Exact factors: 1 in = 2.54 cm, 1 ft = 30.48 cm, 1 lb = 0.45359237 kg. Software bounds (height 80–275 cm, waist/hips 30–300 cm, neck 10–100 cm, weight 20–500 kg) are not clinical reference ranges. Invalid percentages are rejected, not clamped.
These descriptive reference values are not diagnostic thresholds, recommended targets or an assessment of your result. No category is assigned to you.
| Source category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese (source label) | 25%+ | 32%+ |
Source labels and integer ranges are reproduced as descriptive context, not continuous diagnostic cutoffs. Category table reference.
| Age (years) | Men: mean | Women: mean |
|---|---|---|
| 20–39 | 26.1% | 37.8% |
| 40–59 | 28.6% | 40.5% |
| 60–79 | 30.8% | 42.4% |
| 80+ | 30.7% | 40.4% |
Source: NCHS, Series 11 No. 250, Table 3, printed page 12 (all race/ethnicity groups combined). These are historical measured population means, not “ideal” values or current/global norms, and are not directly interchangeable with a formula estimate. CDC/NCHS report and methodology.
Measurements stay in browser memory without uploads or storage.
Enter your values locally; no inputs are uploaded.
Check validation feedback before reviewing the browser-generated result.
Review the explanation, copy supported outputs or reset the workspace.
For ages 20+. Enter height and waist circumference measured at the top of the hip bone, choose the published sex parameter and confirm age eligibility. Estimate, review limitations, copy or reset.
Clear validation, full-width responsive controls, useful advanced options and private browser-local results.
Processing stays in your browser without uploads or storage.
Relative Fat Mass (RFM), published by Woolcott and Bergman in Scientific Reports 8, 10980 (2018), DOI 10.1038/s41598-018-29362-1. RFM = 64 − 20 × (height / waist) + 12 × sex; sex is 0 for male or 1 for female.
Only standing height and waist circumference, plus the published equation parameter and confirmation of age 20+. No weight, neck, hip or age value is used in the equation.
Use a horizontal tape around the bare trunk at the top of the hip bone, at the end of a normal breath out. This follows the study location, not the narrowest waist. Do not compress the skin.
Yes. Choose imperial inches or metric centimeters. Calculations use exact international length conversions and retain original unrounded measurements when display units change.
RFM is a statistical estimate, not a direct measurement. The model was developed in US adults aged 20–85 and validated in ages 20–69. Accuracy varies by population, age, body composition and measurement technique.
No. It provides no health classification, ideal body-fat target or weight-loss recommendation. Software input bounds are not clinical reference ranges, and invalid percentage outputs are rejected without clamping.