How accurate is the US Navy method?

When the tape measurements are taken carefully, it typically lands within a few percentage points of lab methods like DEXA or hydrostatic weighing. It’s most useful for tracking change over time: measure the same way, at the same time of day, and watch the trend rather than the single number.

How do I take the measurements correctly?

Measure the neck just below the larynx (Adam’s apple), the waist at the navel for men or at the narrowest point for women, and the hips at their widest point. Keep the tape level and snug without compressing the skin, and stand relaxed — don’t suck in.

What’s a healthy body fat percentage?

It depends on sex and age. As a broad guide from the American Council on Exercise, 6–13% is athletic and 14–24% typical for men, while 14–20% is athletic and 21–31% typical for women; above roughly 25% for men and 32% for women is classed as obese. These are conventions, not sharp medical lines.

Why do women enter a hip measurement but men don’t?

The Navy method uses separate equations by sex because fat is distributed differently. Women tend to store proportionally more fat around the hips, so the female equation adds the hip circumference (waist + hip − neck) to capture it.

Why does my smart scale show a different number?

Smart scales estimate body fat from a small electrical current (bioelectrical impedance), which swings noticeably with hydration, food, and recent exercise. The tape method responds to different errors. Both are estimates — pick one method and track it consistently instead of comparing across methods.

Can body fat be too low?

Yes. Roughly 2–5% for men and 10–13% for women is considered essential fat — the minimum needed for hormones, organs, and immune function. Sustained levels near those floors can disrupt health, so very lean targets belong under professional supervision.

No — the calculation runs entirely in your browser. Your measurements are never sent to a server or stored.

Body Fat Percentage Calculator

Estimate body fat percentage using the US Navy method.

Runs in your browser — files never leave your device

Sex

HeightcmNeckcmWaistcm

Body fat

18.4%

How it works

This tool estimates the share of your body weight that is fat, using the US Navy circumference method — an approach developed for the Navy in the 1980s so body composition could be checked with nothing but a tape measure. It works from the sizes of your neck, waist, and (for women) hips relative to your height.

The exact equations the calculator runs, with all lengths in centimeters and log10 meaning the base-10 logarithm: for men, body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450; for women, body fat % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height)) − 450. The result is rounded to one decimal place.

Worked example: a man 180 cm tall with a 40 cm neck and a 90 cm waist. Waist minus neck is 50 cm, log10(50) ≈ 1.699 and log10(180) ≈ 2.255, so the divisor is 1.0324 − 0.19077 × 1.699 + 0.15456 × 2.255 ≈ 1.0569. Then 495 ÷ 1.0569 ≈ 468.4, and 468.4 − 450 gives 18.4% — the number the tool shows for those inputs.

When reading the result, remember that healthy levels differ by sex: women naturally carry more essential fat than men, so identical percentages mean different things. Rather than chasing one “perfect” number, compare yourself against typical ranges for your sex (see the FAQ below) and track how your own value moves over weeks and months.

Limitations: a tape-based estimate is sensitive to technique — tape position, tension, time of day, and bloating all shift the result — and it’s least reliable at very lean or very high body-fat extremes. Lab methods such as DEXA remain the reference standard. Treat the output as general guidance only — not medical advice; consult a professional before acting on it.

Frequently asked questions

How accurate is the US Navy method?: When the tape measurements are taken carefully, it typically lands within a few percentage points of lab methods like DEXA or hydrostatic weighing. It’s most useful for tracking change over time: measure the same way, at the same time of day, and watch the trend rather than the single number.
How do I take the measurements correctly?: Measure the neck just below the larynx (Adam’s apple), the waist at the navel for men or at the narrowest point for women, and the hips at their widest point. Keep the tape level and snug without compressing the skin, and stand relaxed — don’t suck in.
What’s a healthy body fat percentage?: It depends on sex and age. As a broad guide from the American Council on Exercise, 6–13% is athletic and 14–24% typical for men, while 14–20% is athletic and 21–31% typical for women; above roughly 25% for men and 32% for women is classed as obese. These are conventions, not sharp medical lines.
Why do women enter a hip measurement but men don’t?: The Navy method uses separate equations by sex because fat is distributed differently. Women tend to store proportionally more fat around the hips, so the female equation adds the hip circumference (waist + hip − neck) to capture it.
Why does my smart scale show a different number?: Smart scales estimate body fat from a small electrical current (bioelectrical impedance), which swings noticeably with hydration, food, and recent exercise. The tape method responds to different errors. Both are estimates — pick one method and track it consistently instead of comparing across methods.
Can body fat be too low?: Yes. Roughly 2–5% for men and 10–13% for women is considered essential fat — the minimum needed for hormones, organs, and immune function. Sustained levels near those floors can disrupt health, so very lean targets belong under professional supervision.
Is my data uploaded?: No — the calculation runs entirely in your browser. Your measurements are never sent to a server or stored.

Body Fat Percentage Calculator

How it works

Frequently asked questions

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