The Most Useful Site in the World⚡ The short version
The US Navy method estimates body-fat percentage from neck circumference, waist circumference and height (plus hip for women). A man with a 37-inch waist, 15-inch neck and 70-inch height is estimated at roughly 19.5% body fat — within the fitness range for adult men.
The calculator
How to use it
- Height — measured, not remembered. Stand against a wall without shoes.
- Neck — measure at the narrowest point, just below the Adam's apple. Keep the tape level and do not pull it tight.
- Waist — at the navel for men, at the narrowest point for women. Measure after a normal exhale, not sucked in.
- Hips (women only) — at the widest point of the hips.
- Read the category, not just the number. The estimate has a margin of error; the category (essential fat, athletes, fitness, average, obese) is more useful than the decimal places.
Worked example
A man, 70 inches tall, 37-inch waist, 15-inch neck. The US Navy formula for men is: body fat % = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76.
Waist minus neck: 37 − 15 = 22 inches. log₁₀(22) = 1.3424, log₁₀(70) = 1.8451. So: 86.010 × 1.3424 − 70.041 × 1.8451 + 36.76 = 115.46 − 129.23 + 36.76 = approximately 19.5%.
For a woman at 64 inches tall, 29-inch waist, 13-inch neck, 38-inch hips: the formula uses waist + hip − neck. The result depends on all four tape measurements and height, which is why women need one extra measurement.
What a tape measure cannot tell you
- Fat distribution. This method gives a single percentage; it says nothing about where the fat sits. Visceral fat (around the organs) carries more health risk than subcutaneous fat, and this method cannot distinguish them.
- Muscle mass changes. If you are building muscle and losing fat at the same time, the tape measurements may not move as fast as your body composition is changing.
- Individual variation. The formula was derived from population data; individual error is commonly ±3–4 percentage points. Use it for trends over weeks, not for a single reading.
- Not for children or pregnant women. The US Navy formula was developed for adults and is not validated for children, adolescents or pregnancy.
🛠️ Related health tools
❓ Frequently asked questions
How does the US Navy body fat method work?
It estimates body-fat percentage from height, neck circumference and waist circumference (plus hip for women). The formula calculates the difference between waist and neck as a proxy for trunk fat, then adjusts for height. It was developed from comparison with hydrostatic weighing and correlates well for most adults.
How accurate is a tape-measure body fat estimate?
Expect roughly ±3–4 percentage points against a DEXA scan. It is accurate enough to track trends over time (which is what matters) and less accurate for a single reading. Measure under the same conditions each time — same time of day, same clothing, same tension on the tape.
What is a healthy body fat percentage?
For men: essential fat 2–5%, athletes 6–13%, fitness 14–17%, acceptable 18–24%, obese 25%+. For women: essential 10–13%, athletes 14–20%, fitness 21–24%, acceptable 25–31%, obese 32%+. These are population ranges — individual health depends on more than a single number.
Why do I need to measure my neck?
Neck circumference accounts for differences in frame size and upper-body muscle mass. A person with a thick neck and a 34-inch waist has a very different body composition from someone with a thin neck and the same waist measurement. Without the neck, the formula would overestimate body fat for muscular builds.
Is body fat percentage better than BMI?
They measure different things. BMI is a screening tool based on height and weight; body fat percentage tries to measure actual fat mass. BMI is faster and needs no measurements; body fat is more informative for individuals, especially muscular people whom BMI misclassifies. Neither is a diagnosis.