Body Fat Calculator
US Navy method. Enter your measurements and get an estimate.
About this tool
Body Fat Calculator
Body Fat Calculator estimates body fat percentage using the US Navy circumference method, in imperial or metric units.
How to use it
- Choose your units and sex.
- Enter your height, waist at the navel, and neck circumference.
- Women also enter hip circumference.
- Read the estimated percentage.
How the Navy method works
The method uses circumference measurements rather than calipers or a scan. It works because fat distributes predictably enough across a population that waist, neck and height together correlate with total body fat.
Accuracy is typically within three or four percentage points against more precise methods, which is respectable for something requiring only a tape measure. It is least accurate at the extremes, for very lean and very heavy people, and for anyone whose build differs markedly from the population it was derived from.
When it helps
- Getting a more useful figure than BMI, since it attempts to separate fat from lean mass.
- Tracking change over months using a consistent method.
- Setting a realistic target with a number that responds to training.
- Estimating without needing a gym or a clinic.
Common mistakes
- Measuring inconsistently. Tape position, tension and time of day all move the result, so what matters is measuring the same way every time.
- Pulling the tape tight. It should sit flush without compressing.
- Treating the number as exact. It is an estimate with real error bars, and the trend matters far more than any single reading.
What this tool handles
- An estimate for general fitness use, not medical advice or a clinical measurement.
