Formula sourced to the Naval Health Research Center, 1984
Measuring tape technique
This calculator only works as well as the three or four numbers you feed it. Measure the neck just below the larynx, the waist at the navel for men, and the hips at their widest point for women, using a flexible tape held snug against the skin but not pulled tight enough to compress it. Take each measurement twice and use the average if the two readings disagree by more than a quarter inch, and measure at roughly the same time of day, since the body shifts water weight over the course of one.
The Navy method's numbers
The formulas below come from a pair of 1984 Naval Health Research Center technical reports by researchers James Hodgdon and Michael Beckett, who built separate circumference-based regressions for men and women against underwater weighing, the body-composition gold standard available at the time.
| Sex | Formula |
|---|---|
| Men | 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76 |
| Women | 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387 |
All measurements go in as inches. The category bands shown in the results panel (essential, athletic, fit, average, high) follow the same ranges the Navy study and later fitness-industry references built around those percentages.
Reading fat mass and lean mass
Enter body weight and the calculator splits it into fat mass and lean mass using the body fat percentage above. Lean mass covers everything that isn't fat: muscle, bone, organs, water. Watching that number alongside the percentage matters most during a cut, since the goal is usually to lose fat mass while holding lean mass steady, not just to see the scale total drop.
More tools for the full picture
- BMI Calculator, for the height-and-weight screening number
- Ideal Weight Calculator, for a healthy weight range by height
- Protein Intake Calculator, to help hold onto lean mass while cutting
Common questions
How accurate is the Navy method compared to a DEXA scan?
It typically lands within about 3 to 4 percentage points of a DEXA scan for most body types, which is the imaging method researchers treat as closer to a gold standard. That is close enough for tracking trends, not close enough for a clinical diagnosis.
Why does the women's formula need a hip measurement?
The original Navy research found that fat distribution differs enough by sex that the men's regression, built from neck and waist alone, didn't hold up as well for women. Adding hip circumference to the women's equation corrected for that.
Can I use this to track progress over time?
Yes, and that is where it is most useful. A single reading has more error than a scale number can show, but measuring the same way, at the same time of day, every few weeks turns the noise into a usable trend.
What happens if my waist is smaller than my neck measurement?
The formula needs waist to exceed neck (plus hip for women) for the logarithm inside it to behave. This calculator floors that difference at 1 so it never breaks, but a genuinely negative difference usually means a measurement was taken incorrectly.