Body Fat Calculator

Measure a few body circumferences with a tape and this estimates your body fat percentage using the U.S. Navy method.

The U.S. Navy method

Developed by the Naval Health Research Center, this method fits an equation to log-transformed circumference measurements. In centimetres:

Men: 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Women: 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450

Because it relies on the tape, technique matters. Measure two or three times and average, keep the tape level, and take readings at the same time of day. Trends over weeks are more meaningful than any single estimate.

Body fat categories

Category	Men	Women
Essential fat	2–5%	10–13%
Athletes	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
Above average	25%+	32%+

Worked example

A man 180 cm tall with a 38 cm neck and 90 cm waist: 495 ÷ (1.0324 − 0.19077 × log₁₀(90 − 38) + 0.15456 × log₁₀(180)) − 450 ≈19% — the top of the "fitness" range. Trimming the waist to 84 cm at the same neck and height brings it to about 15%. Waist size is the biggest lever in this formula, which is also why waist-to-height ratio is a useful companion check.

What to do with the number

Pick one method (this one, calipers, a scan) and stick with it — the direction over weeks matters more than the exact figure. To lower body fat, run a modest calorie deficit with the calorie calculator, keep protein high via the macro calculator, and lift weights so the loss is mostly fat.

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Frequently asked questions

How accurate is the Navy method?

For a tape-and-formula method it is reasonable — typically within about 3 to 4 percentage points of a DEXA scan for most people. It is least reliable at very low or very high body fat, and for people whose fat sits mostly outside the neck, waist and hip.

Where exactly do I measure?

Neck: just below the larynx, tape sloping slightly down at the front. Waist: at the navel for men, at the narrowest point for women. Hip (women only): at the widest point. Keep the tape snug but not compressing the skin, measure on bare skin after a normal breath out, and take each measurement two or three times and average.

What is a healthy body fat percentage?

Rough adult ranges: men about 10 to 20 percent, women about 18 to 28 percent, with trained athletes often below that. 'Essential fat', the minimum needed for health, is around 3 to 5 percent for men and 10 to 13 percent for women — going below it disrupts hormones and immunity.

How does this compare to a smart scale or DEXA?

Bioimpedance scales are convenient but sensitive to hydration, food and time of day, so readings can swing several points day to day — use them only for trends under identical conditions. DEXA is one of the most accurate practical methods and also shows where fat and muscle sit, but it costs money and needs a clinic visit. The Navy tape method is free and, done carefully, close enough to track progress.

Why does the women's formula need a hip measurement?

Women carry a larger and more variable share of body fat around the hips, so including that circumference makes the estimate more accurate. The men's formula uses neck and waist only.

My body fat looks high but my BMI is normal — which is right?

They measure different things. It is possible to have a 'healthy' BMI while carrying an unhealthy amount of fat and little muscle ('normal-weight obesity'). If they disagree, the body fat figure plus your waist-to-height ratio (keep waist under half your height) tells you more than BMI alone.

Last reviewed: September 2026. Figures and formulas are checked against their published sources; see the site's data notes.