Body Fat Calculator
Enter your sex, height, neck, waist, and (for women) hip circumference to get an estimated body fat percentage using the US Navy method.
How It Works
This calculator uses the US Navy circumference method. For men:
body fat % = 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450.
For women:
body fat % = 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.221 x log10(height)) - 450.
All measurements go into the formula in centimeters, so imperial entries are converted
before the calculation runs.
Worked Example
A man who is 180 cm tall with a 38 cm neck and 90 cm waist: waist minus neck = 52 cm. Log10 of 52 is about 1.716, log10 of 180 is about 2.255. Plugging in: 495 / (1.0324 - 0.19077 x 1.716 + 0.15456 x 2.255) - 450 = 495 / (1.0324 - 0.3274 + 0.3487) - 450 = 495 / 1.0537 - 450, which works out to about 19.8 percent body fat.
Frequently Asked Questions
How accurate is the US Navy body fat method?
It is generally accurate within about 3 to 4 percent of body fat compared to more precise methods like DEXA scans, for most body types. It tends to be less accurate for people who are very lean or who carry weight in unusual proportions.
Why does the formula only need three or four measurements?
The method was developed by the US Navy as a fast field measurement using tape-measure circumferences instead of equipment like calipers or scanners, trading some precision for speed and simplicity.
Where exactly should I measure my waist and neck?
Measure the neck just below the larynx, with the tape sloping slightly downward toward the front. Measure the waist at its narrowest point for men, or at the level of the belly button for women. Measure hips at their widest point. Keep the tape snug but not compressing the skin.
Why is hip measurement only used for women?
The original Navy formula was developed and validated separately for men and women, and the women's version includes hip circumference because fat distribution patterns differ between sexes.
Can I use inches instead of centimeters?
Yes. Choose inches from the unit selector and enter your measurements as usual. The calculator converts everything to centimeters internally before applying the formula, since the published coefficients are defined in metric units.
What should I do with my body fat percentage once I have it?
It is most useful as a baseline to track change over time using the same measuring technique, rather than as an exact clinical figure. Re-measure every few weeks under similar conditions to see a trend.