How the Navy method works
The calculator uses the equations of Hodgdon and Beckett (1984), developed at the US Naval Health Research Center and used ever since by the US armed forces to monitor body composition. They estimate body fat from height and neck and waist circumferences in men, and hips as well in women.
| Measurement | Where to place the tape |
|---|---|
| Neck | Just below the Adam's apple |
| Waist (men) | At navel level |
| Waist (women) | At the narrowest part of the torso |
| Hips (women) | At the widest part of the buttocks |
Tips for measuring well
- Measure in the morning, before eating and before training.
- Stand relaxed, without sucking your stomach in and without pulling the tape tight.
- Take each measurement two or three times and use the average.
- Always repeat in the same conditions so you can compare.
How accurate it is
It is a field estimate, not a lab measurement. In the validation by Shake and colleagues (1993) against hydrostatic weighing, in 49 men and 50 women with fairly high body fat, the equation was less accurate at the extremes, and between 6.8% and 18% of the people classed as having excess fat were false positives; the authors advise caution when using it for individual decisions.
Circumference equations are still being reviewed. In 2024, Taylor and colleagues used DXA in 1,904 US Army soldiers to develop new equations that improved on the current ones, especially in men. The most useful thing about this method is the trend: if you measure the same way every few weeks, you will see whether your fat is going up or down even if the exact number has some error.
How to read the result
There are no universally agreed body fat ranges: in 2000, Gallagher and colleagues noted that none existed and proposed provisional ones based on BMI. As a reference, the calculator uses the World Health Organization's body-fat threshold for obesity, more than 25% in men and 35% in women, the same one used in the study by Romero-Corral and colleagues (2008), and tells you whether you are above or below it. You will find charts by age and sex in body fat percentage: chart by age.
Use the result in the other calculators
With your body fat percentage, the maintenance calorie calculator uses the Cunningham equation, based on lean mass, and the protein calculator works from your lean mass if you want to lose fat.
