π Body Fat Calculator
US Navy method estimate from tape measurements.
Category
Estimates only, not medical advice. Talk to a clinician about what your result means for you.
How to Use This Calculator
Choose your unit system and sex, enter your tape measurements, and the calculator applies the US Navy body-fat equations and places you in an ACE fitness category.
Select inches or centimeters, then male or female. Women get an extra hip measurement field.
Measure height standing straight without shoes, neck just below the Adam's apple, waist around the navel after a normal exhale.
Women also measure hips at the widest point around the buttocks.
Read your estimated body fat percentage and category. Re-measure monthly under the same conditions to track trends.
The US Navy Equations
The equations were developed by Hodgdon and Beckett at the Naval Health Research Center from underwater-weighing data. The logic is simple: your waist relative to your neck estimates abdominal fat, and height scales it to body size. For women, hips enter the equation because female fat distribution differs. The logarithms compress the ratios into the percentage range the researchers calibrated. If you enter centimeters, the calculator converts to inches first (divide by 2.54), since the constants were fitted in inches.
Worked Example
A man 70 inches tall, 15-inch neck, 34-inch waist. Waist minus neck = 19. BF% = 86.010 x log10(19) - 70.041 x log10(70) + 36.76 = 86.010 x 1.2788 - 70.041 x 1.8451 + 36.76 = 109.99 - 129.23 + 36.76 = 17.5 percent, just at the top of the fitness band. If his waist were 36 inches instead: 86.010 x log10(21) = 113.78, giving 113.78 - 129.23 + 36.76 = 21.3 percent, solidly average. Two inches at the waist moved the estimate nearly 4 points, which shows why consistent measuring technique matters more than the formula.
Getting Useful Numbers
Measure in the morning before eating, since food and water bloat the waist. Keep the tape level and snug without pinching skin, and breathe normally rather than sucking in. Track the trend, not single readings: a 1-point wobble between measurements is noise, but a steady 3-point drop over two months is real progress. Pair the number with waist circumference itself and how your clothes fit, because all three move together when fat loss is genuine. Remember these are estimates, not medical advice: if the result surprises you or you are planning big body-composition changes, a clinician or dietitian can confirm with professional methods.
Frequently Asked Questions
How accurate is the US Navy body fat method?
Reasonably good for a tape measure: studies find it lands within about 3 to 4 percentage points of DEXA scans for most people, which is similar to decent smart scales and far better than BMI at describing body composition. Accuracy depends entirely on honest measuring: a half-inch error at the waist moves the result by roughly 1 to 2 points. It is a field estimate, not a clinical measurement, and very lean or very heavy bodies stretch its accuracy.
How do I measure my waist, neck, and hips correctly?
Use a soft tape, measure in the morning, and keep the tape snug but not compressing skin. Waist: around the navel (belly button), relaxed, after exhaling normally. Neck: just below the Adam's apple, tape sloping slightly down. Hips (women): the widest point around the buttocks. Height: standing straight without shoes. Take each measurement twice and average them.
What is a healthy body fat percentage?
The American Council on Exercise bands for men: essential fat 2 to 5 percent, athletes 6 to 13, fitness 14 to 17, average 18 to 24, obese 25 and up. For women: essential 10 to 13, athletes 14 to 20, fitness 21 to 24, average 25 to 31, obese 32 and up. "Healthy" for most adults means the fitness to average range. Below essential-fat levels, hormones, immunity, and (in women) menstrual function suffer.
Why do women have higher essential body fat?
Biology: women need extra fat for reproductive function, including breast tissue, hips, and the sex-specific fat that supports pregnancy and breastfeeding. Essential fat is about 10 to 13 percent for women versus 2 to 5 percent for men, which is why the healthy ranges sit roughly 8 to 10 points higher for women at every fitness level. Comparing your number to the opposite sex's chart is meaningless.
Is body fat percentage better than BMI?
For individuals, usually yes. BMI cannot tell muscle from fat, so it mislabels muscular people as overweight and "skinny fat" people as healthy. Body fat percentage measures what you actually care about. That said, where fat sits also matters: visceral belly fat predicts health risk better than total body fat does, which is why waist circumference on its own is also a useful number to track.