Body Fat Calculator

The US Navy body fat method estimates body fat percentage from a handful of tape measurements — height, neck and waist, plus hips for women. It was developed so that the military could assess personnel quickly without expensive equipment, and it remains one of the better no-equipment estimates available, typically landing within three to four percentage points of a DEXA scan for most people. Its logic is that neck and waist circumferences at a given height correlate with the proportion of fat mass. Body fat percentage is a considerably more useful number than BMI, because it distinguishes the tissue that matters from the tissue that does not. Measure carefully — a centimetre of error on the waist moves the result more than most people expect — and use the trend across repeated measurements rather than any single reading.

How this is calculated

The Navy method uses logarithmic regressions. For men, body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. For women the equation adds hip circumference: 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450. All measurements are in centimetres.

Worked example for a man at 180 cm with a 85 cm waist and 38 cm neck: waist minus neck is 47 cm, and the equation returns roughly 18% body fat.

The women's formula includes hips because fat distribution differs, and a waist measurement alone would systematically misestimate. This is why the two equations are not interchangeable.

How to measure so the number means something

Waist: for men, at the navel; for women, at the narrowest point of the torso. Keep the tape horizontal and snug without compressing the skin, and measure at the end of a normal exhale rather than holding your breath in.

Neck: just below the larynx, with the tape sloping slightly downward at the front. Hips, for women: at the widest point of the buttocks.

Consistency matters more than absolute precision. Measuring at the same time of day, in the same conditions, using the same landmarks, makes the trend across weeks reliable even if any single reading is a little off.

What body fat percentage is healthy?

Commonly cited ranges for men are 6% to 13% for athletes, 14% to 17% for fit, 18% to 24% acceptable, and 25% and above obese. For women the equivalent ranges run roughly ten points higher — 14% to 20% for athletes, 21% to 24% fit, 25% to 31% acceptable, and 32% and above obese.

Women carry more essential fat than men for physiological reasons, which is why the ranges differ rather than one scale applying to everyone. Very low body fat is not a health goal in either sex; below the athletic range it carries real costs to hormonal function, immunity and bone density.

How to use the body fat calculator

Select your sex. The formulas differ, and the women's version requires a hip measurement as well.
Measure height, neck and waist in centimetres. Use a flexible tape, snug but not compressing. Measure at the end of a normal exhale.
Track the trend, not the reading. A single measurement carries a few points of uncertainty. Repeat under the same conditions every couple of weeks and watch the direction.

Frequently asked questions

How do I measure correctly?

Neck: just below the larynx, tape sloping slightly down at the front. Waist: at the navel for men, at the narrowest point for women, after a normal exhale. Hip (women): at the widest point.

What is a healthy body fat percentage?

Typical healthy ranges: men 10–20%, women 18–28%. Athletes run lower; essential fat is about 3% for men and 12% for women.

How accurate is the Navy method?

Typically within three to four percentage points of a DEXA scan for most people — good enough to track progress, not precise enough to obsess over a single reading. It is less reliable at the extremes of body composition, where the underlying regressions were fitted on fewer people.

Why do women need a hip measurement and men do not?

Because fat distribution differs. Women carry a greater proportion on the hips and thighs, which a waist measurement alone would miss, so the women's equation includes hip circumference to capture it. The two formulas are not interchangeable.

Is body fat percentage better than BMI?

For an individual, yes. BMI cannot distinguish muscle from fat, so a muscular person and a sedentary one of identical height and weight get the same score. Body fat percentage measures the tissue that actually relates to metabolic risk.