Body fat calculator
Estimate body fat with a tape measure. US Navy method.
How it works
The US Navy method uses waist, neck and height (plus hip for women). Expect a few points of error either way. It is an estimate, not a scan.
How to read your result
The result is the share of your body weight that is fat, estimated with a tape measure. The method uses equations the US Navy developed in 1984, and the US Army's tape test is built on them. It takes your height, your neck and your waist, plus your hips if you are a woman.
It is an estimate. These military equations are reported to have a typical error (standard error) of 3 to 4 percentage points, so treat 20% as a rough position, not an exact figure. The equations tend to read too high at low body fat and too low at high body fat. In a study of 481 women and 926 men starting Army basic training, tape results were on average 6 points lower than a DXA body scan. For women, big glute muscles can push the hip measurement up and make the result read too high.
Use it to see roughly where you stand. The American Council on Exercise (ACE) calls 18 to 24% typical for a man who is not an athlete, and 25 to 31% typical for a woman who is not an athlete. Do not use it to track small changes. In the same Army study, a DXA scan showed body fat falling by about 4 points in women over 8 weeks, while the tape showed no change. Measure the same way each time: trained testers repeat the tape measurement to within 1 point.
A worked example
Example, man: 180 cm tall (70.9 in), waist 90 cm (35.4 in), neck 38 cm (15.0 in). Step 1: waist minus neck = 90 − 38 = 52. Step 2: log10(52) = 1.7160 and log10(180) = 2.2553. Step 3: 1.0324 − 0.19077 × 1.7160 + 0.15456 × 2.2553 = 1.0324 − 0.32736 + 0.34857 = 1.05361. Step 4: 495 ÷ 1.05361 = 469.81, then 469.81 − 450 = 19.81. The calculator shows 19.8%, inside ACE's 18 to 24% range for a man who is not an athlete. A small tape slip matters: a waist of 91 cm gives 20.5%, and 89 cm gives 19.1%.
Example, woman: 165 cm tall (65.0 in), waist 75 cm (29.5 in), hips 98 cm (38.6 in), neck 32 cm (12.6 in). Step 1: waist + hips − neck = 75 + 98 − 32 = 141. Step 2: log10(141) = 2.1492 and log10(165) = 2.2175. Step 3: 1.29579 − 0.35004 × 2.1492 + 0.221 × 2.2175 = 1.29579 − 0.75231 + 0.49006 = 1.03354. Step 4: 495 ÷ 1.03354 = 478.94, then 478.94 − 450 = 28.94. The calculator shows 28.9%, inside ACE's 25 to 31% range for a woman who is not an athlete. The inch values are rounded; the calculator converts exactly.
How accurate is the US Navy body fat calculator?
The military tape equations are reported to have a standard error of 3 to 4 percentage points. Against a DXA scan, tape results averaged about 6 points lower in 1,407 young Army recruits. Treat the result as a rough guide.
Where do I measure my waist, neck and hips?
Use a flexible tape held flat on the skin with steady tension. In the military method, men are measured at the neck and at the belly at the level of the navel (enter that in the waist box). Women are measured at the neck, at the waist (the narrowest part of the torso) and at the hips (the widest part of the buttocks).
What is a normal body fat percentage?
ACE calls 18 to 24% typical for a man who is not an athlete and 25 to 31% typical for a woman. ACE says below 6% for men or 14% for women may be dangerously low. It counts 25% or more for men and 32% or more for women as obesity.
Does Zefro use my body fat to set my calories?
No. Zefro's calorie and macro targets come from your sex, age, height, weight, activity level and goal. Body fat is not an input. Zefro's own Navy estimate uses the same formula as this page.