Body Fat Percentage Estimator
Estimate your body fat percentage from simple tape measurements using the US Navy method or Relative Fat Mass (RFM) -- with approximate fat mass and lean mass. Everything is calculated in your browser.
Your Details
Measurements
With neck (and hip, for women) the US Navy method is used; with waist only, Relative Fat Mass (RFM) is used. Measure the waist at the navel (men) or narrowest point (women), relaxed.
Health note: This is a consumer estimate, not a clinical body-composition measurement. Results can differ significantly from DEXA scans, professional assessments and other methods. It is for adults and is not suitable during pregnancy. Speak to a healthcare professional for an accurate assessment.
Results
Estimated body fat
Method:
Estimated fat mass
Estimated lean mass
General reference ranges (American Council on Exercise)
| Description | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Above average | 32% + | 25% + |
Reference ranges are general and do not account for age or ethnicity. Fat mass = weight × body fat %; lean mass = weight − fat mass.
How this calculator works
US Navy method (measurements in cm): men 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450; women 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. Relative Fat Mass: 64 − 20 × (height ÷ waist), plus 12 for women. Imperial measurements are converted to centimetres first. Fat mass and lean mass are derived from your weight and the estimated percentage, rounded to one decimal place.
How accurate is this body fat estimate?
It is an estimate. Circumference-based formulas typically differ from lab methods such as DEXA scans or underwater weighing by several percentage points, and more for some body types. Measurement technique matters a lot. Use the result to follow a trend over time with consistent measurements, not as a clinical measurement.
Which methods are used?
If you enter your neck measurement (and hips, for women), the calculator uses the US Navy circumference method (Hodgdon & Beckett, 1984). Otherwise it uses Relative Fat Mass, or RFM (Woolcott & Bergman, 2018): 64 − 20 × (height ÷ waist), plus 12 for women. When both are possible, you see both.
How should I measure?
Use a flexible tape, keep it level and snug but not tight, and measure on bare skin. Waist: at the navel for men, and at the narrowest point for women (the Navy method's convention), relaxed, after breathing out. Neck: just below the larynx (Adam's apple). Hips: at the widest point of the buttocks. Measure two or three times and use the average.
Is my data stored or shared?
No. All measurements stay in your browser. Nothing is sent to our servers, stored or included in analytics.
Disclaimer: This calculator is for general information only and is not medical advice, diagnosis or treatment. See our Disclaimer and Terms of Use for more detail.