Body fat calculator
The U.S. Navy tape-measure method: height, neck and waist (plus hips for women). No calipers, no smart scale, just a tape.
Enter height, neck and waist to see your estimate.
What moves the number: the waist
The Navy formula uses the logarithm of waist minus neck. Neck barely changes as you lean out, so the waist carries the estimate. Drag to see what a smaller (or bigger) waist would do to your result.
The Navy body fat formula
Developed by Hodgdon and Beckett at the Naval Health Research Center (1984) and still used for U.S. military body-composition standards, with measurements in inches:
- 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
This calculator converts centimetres for you. For the best tracking, measure on the same morning each check-in and log it in the measurement tracker; this page then pre-fills itself. To turn the result into muscle numbers, try the FFMI calculator or lean body mass calculator.
ACE body fat categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Questions people ask
How accurate is the Navy body fat calculator?
The U.S. Navy circumference method (Hodgdon & Beckett, Naval Health Research Center, 1984) typically lands within about 3–4 percentage points of hydrostatic weighing for most people. It is less accurate for very lean or very muscular builds and for people who carry fat unusually. Its real strength is tracking change: measured the same way each time, the trend is reliable.
Where do I measure for the Navy method?
Neck just below the larynx (Adam’s apple), tape angled slightly down at the front. Men measure the waist horizontally at the navel; women at the narrowest point of the waist, plus hips at the widest point of the buttocks. Stand relaxed and don’t suck in.
What is a healthy body fat percentage?
The American Council on Exercise (ACE) chart puts “fitness” at 14–17% for men and 21–24% for women, and “average” at 18–24% for men and 25–31% for women. Essential fat is about 2–5% for men and 10–13% for women; going near those levels is not healthy long term.
Why does my body fat estimate barely change when I lose weight?
The formula is driven by waist minus neck. If most early loss is water, the waist moves little. As fat comes off your midsection, the estimate drops. Around 2.5 cm (1 in) off the waist typically lowers the estimate by roughly 1.5–2.5 points.