Navy Body Fat Calculator
Enter your height, neck, waist (and hip if female), and weight to estimate your body fat percentage using the U.S. Navy circumference method — no calipers or scans required, just a tape measure.
How this calculation works
The Navy method estimates body fat from a handful of circumference measurements plugged into a logarithmic regression formula originally developed for military fitness screening. Every measurement is converted from centimetres to inches before the calculation, since the original formula was built and validated in imperial units.
For men, the formula uses waist minus neck circumference and height: body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. For women, it adds hip circumference: body fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450.
Once body fat percentage is known, fat mass is your weight multiplied by that percentage, and lean mass (muscle, bone, organs, water) is whatever remains: weight minus fat mass.
Worked example
Body fat categories by sex
These American Council on Exercise-style bands are the standard reference for interpreting a Navy body fat result:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 – 5% | 10 – 13% |
| Athletic | 6 – 13% | 14 – 20% |
| Fitness | 14 – 17% | 21 – 24% |
| Average | 18 – 24% | 25 – 31% |
| Obese | 25%+ | 32%+ |
Navy method vs. BMI
BMI only compares weight to height, so it cannot tell muscle from fat — a heavily muscled person and a person carrying excess fat can share the same BMI. The Navy method instead measures circumferences tied directly to fat distribution, so it distinguishes a lean, muscular build from a fat-dominant one far better than BMI alone.
That said, the Navy method still has blind spots: it does not see visceral (internal) fat directly, and results depend heavily on careful, consistent measurement technique. Use it alongside BMI and, ideally, a periodic professional body-composition scan.
Getting an accurate measurement
- Use a flexible, non-stretch tape measure, not a metal one.
- Measure directly against skin or a single thin layer of clothing, not over bulky clothes.
- Keep the tape parallel to the floor and snug but not compressing the skin.
- Measure at the same time of day (ideally morning, before eating) for consistent tracking over time.
- Take each measurement two to three times and use the average.
What to do with your result
A single reading is a snapshot; the real value comes from tracking the trend over weeks and months as you retest with the same technique. If your body fat and lean mass move in the direction you want — fat down, lean mass steady or up — your training and nutrition are working, even if the scale barely moves.