How the US Navy method works
The formula was developed by the United States Navy to screen service members without special equipment. It uses height, neck and waist for men, and adds hips for women, then converts the logarithms of those lengths into a body fat percentage. All inputs are in centimetres in this tool.
It is far cheaper than a DEXA scan or underwater weighing. The trade off is accuracy. Expect an error of about three to four percentage points compared with a clinical scan, so use it to follow your own trend over weeks.
How to measure correctly
- Stand relaxed and breathe out normally. Do not pull your stomach in.
- Neck: measure just below the larynx, tape sloping slightly down toward the front.
- Waist: men measure at the navel, women at the narrowest point above the navel.
- Hips: measure around the widest part of the buttocks.
- Take each measurement twice and use the average. Measure in the morning before food.
Body fat categories
These ranges follow the American Council on Exercise guide. Women carry more essential fat than men, so their ranges are higher.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5% | 10 to 13% |
| Athletes | 6 to 13% | 14 to 20% |
| Fitness | 14 to 17% | 21 to 24% |
| Average | 18 to 24% | 25 to 31% |
| Above average | 25% and above | 32% and above |
Sleep and body composition
In a controlled trial published in Annals of Internal Medicine in 2010, dieters who slept 5.5 hours lost 55 percent less fat and more lean mass than dieters who slept 8.5 hours, even though calories were the same. If you are trying to lose fat, protect your sleep. Use the bedtime calculator to plan it.