Using the US Navy Body Fat Calculator

This calculator (see bottom of page) uses the U.S. Navy Circumference Method, a simple and quick method that has been shown to be as accurate as skinfold caliper tests, but with a lower standard error of estimation.
Formulae developed by Hodgdon and Beckett at the Naval Health Research Center (1) take into account differences in the way men and women accumulate fat, thus different measurements are required.


How to measure
Measurements within 0.5 cm or 1/4 inch are required. The tape should be tight, but not compress the skin

• Waist:
• Men: measure horizontally, at the level of the navel, which roughly coincides with the hip. Note this is not the minimum circumference.
• Women: measure horizontally, at the level of minimal abdominal width

• Neck (both): measure below the larynx with the tape sloping slightly downward to the front.

• Hips (Women only): Largest horizontal circumference around the hips

Interpretation

Body fat
The American Council on Exercise uses the following categories based on percentage of body fat: 

	Women	Men
Essential fat	10-12%	2-4%
Athletes	14-20%	6-13%
Fitness	21-24%	14-17%
Acceptable	25-31%	18-25%
Obese	32% or more	26% or more

BMI
BMI is simply is the ratio of your weight to the square of your height, with ranges falling under 4 categories. While widely used, it has its limitations - is does not diferentiate by gender, and does not consider fat/muscle ratios. If your BMI is 25 or greater, your waist/height ratio is less than 0.5 and % body fat falls within the  "athlete" or "fitness" categories, you are probably muscular and not fat.

Underweight	BMI less than 18.5
Normal weight	BMI 18.5 to 24.9
Overweight	BMI 25 to 29.9
Obese	BMI 30 or greater

Body Fat Formulae

(Cm):
Men	Percentage of Fat = 495 / (1.0324 - 0.19077 x (LOG10(waist - neck)) + 0.15456 x (LOG10(height))) - 450
Women	Percentage of Fat = 495 / (1.29579 - 0.35004 x (LOG10(waist + hip - neck)) + 0.22100 x (LOG10(height))) - 450
(Inch):
Men	Percentage of Fat = (86.01 x LOG10((waist) - (neck))) - (70.041 x LOG10(height)) + 36.76
Women	Percentage of Fat = (163.205 x LOG10((waist) + (hip) - (neck))) - (97.684 x LOG10(height)) - 78.387

(1) Hodgdon, J. and Beckett, M. Prediction of percent body fat for U.S. navy men and women from body circumferences and height. Reports No. 84-29 and 84-11. Naval Health Research Center, San Diego, California 1984

Thanks to ramui.com for provision of JavaScript and formulae.