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Free Body Fat Percentage Calculator

Estimate your body fat percentage using the U.S. Navy circumference method from simple tape-measure inputs (height, neck, waist, and hip for women), all in centimeters.

Body fat (U.S. Navy method)
18.4%Average

Estimated with the U.S. Navy circumference formula and American Council on Exercise categories. This is an estimate, not a clinical body-composition measurement.

Estimate only. This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

Quick answer

The U.S. Navy method estimates body fat from body circumferences and height. For men: BF% = 495 / (1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height)) − 450. For women: BF% = 495 / (1.29579 − 0.35004·log10(waist + hip − neck) + 0.22100·log10(height)) − 450, with all measurements in centimeters. The result is an estimate, not a clinical measurement.

Formula & method

Enter your sex, then measure with a flexible tape in centimeters: height; neck circumference just below the larynx; and natural waist (at the navel for men, at the narrowest point for women). Women also enter hip circumference at the widest point. The calculator applies the U.S. Navy circumference formula using base-10 logarithms (Math.log10). For men it uses waist minus neck; for women it uses waist plus hip minus neck. The resulting percentage is mapped to a category using American Council on Exercise (ACE) reference ranges, which differ for men and women. Because body fat cannot be negative, results are floored at 0%, and the waist must be larger than the neck for a valid estimate.

Examples

Example 1: Man: 180 cm, neck 40, waist 90
Input
sex = male, height = 180 cm, neck = 40 cm, waist = 90 cm
Result
≈ 18.4% — Average
Why
waist − neck = 50. log10(50) = 1.69897, log10(180) = 2.25527. Denominator = 1.0324 − 0.19077×1.69897 + 0.15456×2.25527 = 1.05686. BF% = 495 / 1.05686 − 450 = 18.37, which rounds to 18.4%. With ACE male ranges (Fitness 14–17%, Average 18–24%), 18.4% falls in the Average band.
Example 2: Man: 175 cm, neck 38, waist 85
Input
sex = male, height = 175 cm, neck = 38 cm, waist = 85 cm
Result
≈ 16.9% — Fitness
Why
waist − neck = 47. log10(47) = 1.67210, log10(175) = 2.24304. Denominator = 1.0324 − 0.19077×1.67210 + 0.15456×2.24304 = 1.06036. BF% = 495 / 1.06036 − 450 = 16.94, which rounds to 16.9%. Since 16.9% is below 18%, this maps to the Fitness category.
Example 3: Woman: 165 cm, neck 32, waist 75, hip 95
Input
sex = female, height = 165 cm, neck = 32 cm, waist = 75 cm, hip = 95 cm
Result
≈ 27.4% — Average
Why
waist + hip − neck = 75 + 95 − 32 = 138. log10(138) = 2.13988, log10(165) = 2.21748. Denominator = 1.29579 − 0.35004×2.13988 + 0.22100×2.21748 = 1.03645. BF% = 495 / 1.03645 − 450 = 27.43, which rounds to 27.4%. Since 27.4% is below 32%, this maps to the Average category for women.

When to use this tool

  • Getting a no-equipment estimate of body fat using only a tape measure at home.
  • Tracking changes in body composition over time alongside weight and waist measurements.
  • Comparing a rough body-fat figure against general fitness categories before talking to a trainer or clinician.

Common mistakes

  • Mixing units. The metric Navy formula expects every measurement in centimeters; entering height in meters (1.8 instead of 180) or a waist in inches gives a meaningless result.
  • Measuring the waist or neck in the wrong place. The neck is taken just below the larynx and the waist at the navel (men) or narrowest point (women); pulling the tape too tight or too loose shifts the estimate by several points.
  • Forgetting hip circumference for women. The female formula requires waist, neck, and hip; leaving hip out makes the calculation invalid.
  • Treating the Navy estimate as a clinical body-composition reading. It is a circumference approximation and can differ from DEXA or hydrostatic weighing by several percentage points.

Frequently asked questions

What is the U.S. Navy body fat method?

It is a formula developed by the Naval Health Research Center that estimates body fat percentage from body circumferences (neck, waist, and hip for women) and height, using base-10 logarithms. It is popular because it needs only a tape measure.

How accurate is the Navy body fat calculator?

For most people it lands within about 3–4 percentage points of laboratory methods like DEXA or hydrostatic weighing. Accuracy depends heavily on measuring at the correct anatomical landmarks; it is an estimate, not a diagnosis.

Why do men and women use different formulas?

Men and women carry fat differently, so the equations use different coefficients. The female version also adds hip circumference because it improves the estimate for typical female fat distribution.

Where exactly should I measure?

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 the widest point for women. Keep the tape level and snug but not compressing the skin.

What is a healthy body fat percentage?

Using American Council on Exercise ranges, fitness levels are roughly 14–17% for men and 21–24% for women, with athletes lower and the average population higher. Healthy targets vary by age, sex, and individual goals, so discuss yours with a professional.

Is this body fat result medical advice?

No. This tool provides a general estimate for information only. It is not a diagnosis or a treatment plan. Consult a qualified healthcare professional for personalized guidance.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

Disclaimer

This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

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Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

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