Body Fat Calculator (U.S. Navy Method)
Your body fat percentage is a far better picture of your health than weight alone — two people of the same weight can carry very different amounts of fat. This free calculator uses the U.S. Navy method, a tape-measure formula developed by the U.S. military that estimates body fat from three simple circumference measurements. All you need is a flexible tape measure and about a minute.
Body Fat Calculator
How to Use This Calculator
Choose your sex and your preferred units, then measure yourself with a flexible (not metal) tape measure. Take all measurements directly against bare skin, keeping the tape snug but never compressing the skin. Measure each site twice and use the average of the two readings.
Measure your neck just below the larynx, sloping slightly downward at the front. Measure your waist at navel level, relaxed, after a normal breath out. Women also measure their hips at the widest point of the buttocks — the female formula uses the hip measurement, so the hip field appears automatically when you select Female.
Enter your height, neck, waist and hip measurements and click Calculate. The tool returns your estimated body fat percentage and the category it falls into, using the standard male and female ranges. Click Reset to clear everything and start over.
The Formula
Men: body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: body fat % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
All measurements are converted to centimeters before the formula runs, and the result is clamped between 2% and 60%. The categories used are: men — essential fat 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obese 25% and up; women — essential fat 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obese 32% and up.
Worked example: a man with a 38 cm neck, 85 cm waist and 170 cm height. Waist minus neck is 47 cm, and log10(47) = 1.67210 while log10(170) = 2.23045. Body fat = 495 ÷ (1.0324 − 0.19077 × 1.67210 + 0.15456 × 2.23045) − 450 = 495 ÷ (1.0324 − 0.31898 + 0.34473) − 450 = 495 ÷ 1.05815 − 450 ≈ 17.8% — right at the boundary between the Fitness (14–17%) and Average (18–24%) ranges for men.
Tips
Measure at the same time of day, ideally in the morning before eating or drinking — hydration and food shift the numbers by a percent or two. Keep the tape horizontal and level all the way around; a twisted tape adds error fast.
Take each measurement twice and use the average. If your two readings differ by more than half an inch, measure a third time. Consistent technique matters far more than precision to the millimeter, and it is what makes week-to-week comparisons meaningful.
Track the trend, not the single number. A change of 1–2 percentage points is enough to see progress, while day-to-day readings bounce around with hydration. Combined with a waist measurement that trends downward, your body fat estimate is a reliable progress gauge.
Frequently Asked Questions
How accurate is the U.S. Navy body fat method?
Studies have found the U.S. Navy method comes within about 3 to 4 percentage points of hydrostatic (underwater) weighing, the former gold standard, for most people. How carefully you place the tape matters more than precision to the millimeter, so measure each site twice and use the average.
How do I measure my neck, waist and hips correctly?
Measure against bare skin with a flexible tape that stays horizontal and snug but never compresses the skin. Neck: just below the larynx, sloping slightly downward at the front. Waist: at navel level, relaxed, after breathing out normally. Hips (women only): at the widest point of the buttocks. Average two readings at each site.
What is a healthy body fat percentage?
For men, roughly 10 to 20% is a healthy range, with athletes often at 6 to 13%. For women, the healthy range is about 20 to 31%, with athletes at 14 to 20%. Everyone needs a minimum of essential fat — about 2 to 5% for men and 10 to 13% for women — for basic bodily functions.
Why do men and women have different body fat standards?
Women carry essential fat in breast tissue, the uterus and other sex-specific deposits that men do not have, so healthy ranges are roughly 8 to 10 percentage points higher for women. The male and female formulas in this calculator reflect those differences in the math itself.
How fast can I safely lose body fat?
A safe, sustainable pace is about 0.5 to 1% of your body weight per week — roughly 1 to 2 pounds (0.5 to 1 kg). Losing faster tends to shed muscle and can slow your metabolism. Combine a modest calorie deficit with strength training and enough protein to preserve muscle while the fat comes off.