Health
Body fat calculator
This page uses the US Navy circumference method. You need a tape measure for the neck and waist, and for women the hips too.
What this means
- The Navy method estimates 17.5% body fat, which is 31.5 lb of fat and 148.5 lb of everything else.
- Tape methods can be off by a few points. Measure the same way each time and watch the trend.
What if
About this calculator
What this calculator does
It uses the circumference equations the Department of Defense printed in DoD Instruction 1308.3 (2002), which come from Navy research by Hodgdon and Beckett (1984). The military now uses other methods, so this is a field estimate, not a current military standard. All measures are in inches inside the formula.
How it is calculated
men: %BF = 86.010 * log10(waist - neck) - 70.041 * log10(height) + 36.76
women: %BF = 163.205 * log10(waist + hip - neck) - 97.684 * log10(height) - 78.387
How to read the result
The result is the estimated share of your weight that is fat. Fat mass and lean mass split your weight using that share.
How to measure
Measure on bare skin with a flexible tape, snug but not compressing. Take each measure twice and use the average.
Sources and method
Circumference equations in inches from DoD Instruction 1308.3 (2002), Enclosure 3, which come from Navy research by Hodgdon and Beckett (1984). The 1984 reports give a body density equation in centimeters; the inch form used here is the Department of Defense fit and is usually within about 2 percentage points of the density form. The military now uses other methods (a waist-to-height ratio since January 1, 2026, per HPRC), so this is a field estimate, not a current military standard.
- DoD Instruction 1308.3 (2002), DoD Physical Fitness and Body Fat Programs Procedures, Enclosure 3 (unofficial copy)
- Hodgdon and Beckett, 1984, Prediction of percent body fat for U.S. Navy men (NHRC 84-11)
- Hodgdon and Beckett, 1984, Prediction of percent body fat for U.S. Navy women (NHRC 84-29)
- HPRC (DoD), How the military measures body composition
Questions
Does the military still use this method?
No. As of January 1, 2026, the military uses a waist-to-height ratio, according to the DoD's HPRC. This page keeps the tape equations because they are a widely used field estimate.
How accurate is the Navy method?
It is a field estimate. Lab methods such as DEXA are more precise, but tape results are useful for tracking change.
Why do women measure hips?
The published formula for women includes hip circumference.
Does weight change the percentage?
No. Weight is only used to split it into fat mass and lean mass.
Where exactly is the waist?
For men, at the navel. For women, at the narrowest point of the torso.