Body Fat Calculator
Free Body Fat Calculator. Calculate your body fat percentage using the U.S. Navy method and check your body fat category instantly.
What does this Body Fat Calculator do?
This calculator estimates body fat percentage using the U.S. Navy circumference method — a tape-measure-based technique developed by the US Navy as a practical field alternative to lab equipment like DEXA scans or hydrostatic weighing.
The formula
The Navy method uses logarithms of your waist, neck, and (for women) hip measurements along with height. It's more complex than a simple ratio, which is part of why it correlates reasonably well with more expensive lab methods despite only requiring a tape measure.
Step-by-step example
For a man who is 175 cm tall with an 85 cm waist and 38 cm neck, the formula uses log₁₀ of the difference between waist and neck measurements, along with log₁₀ of height, to estimate body fat percentage — typically landing somewhere in the high teens to low twenties for an average-build adult male.
Tips & common mistakes
- Measurement technique matters a lot — measure at the same time of day, same tension on the tape, and the exact same landmark each time for consistent tracking.
- This method is best used to track trends over weeks and months, not as a one-time precise number — a single measurement can be off by a few percentage points.
- Women need an additional hip measurement that men don't, since fat distribution patterns differ meaningfully by sex.
Frequently asked questions
It's a tape-measure estimate, typically within a few percentage points of more precise methods like DEXA scans — accurate enough to track trends, not exact enough for clinical use.