Why do men and women use different formulas?

Fat distribution patterns differ by sex on average, and the formula accounts for that by using different measurement points and coefficients.

What's a healthy body fat range?

This varies by age, sex, and fitness goals — the tool's category labels (essential, athletic, fitness, average, obese) reflect commonly cited ranges, but a healthcare provider can give personalized guidance.

Why does the formula use neck and waist measurements?

Fat tends to accumulate at the waist while the neck stays relatively stable, so the difference between the two correlates with body fat — it's an indirect proxy, not a direct fat measurement.

Is this the same method the military currently uses?

It's the classic 1984 Hodgdon-Beckett formula the U.S. Navy popularized and that this calculator implements; official military body-composition procedures have evolved over time and may differ in measurement sites from what's shown here.

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Health & Fitness

Body Fat Calculator

Body fat percentage using the U.S. Navy tape method.

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About the Body Fat Calculator

Estimates body fat percentage using the U.S. Navy circumference method, which relies on neck, waist, and (for women) hip measurements rather than a scale — used by the U.S. military for decades because it needs no special equipment.

How to use it

Select your Sex.
Enter your Height, Neck, and Waist measurements in cm.
If female, also enter your Hip measurement.
Read your estimated body fat percentage and category in the result panel.

Formula

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

Hodgdon & Beckett circumference method (Naval Health Research Center, 1984), developed and validated against U.S. Navy and Army personnel. Independent research finds it correlates reasonably well with lab methods for group averages, but tends to underestimate body fat in men and overestimate it in lean women — useful for tracking trends, not a precise individual measurement.

Worked example

A man with a 38cm neck, 85cm waist, and 175cm height comes out to roughly 16–18% body fat, depending on rounding.

Recommendations

• Measure at the same time of day and the same way each time — small measuring differences shift the result noticeably.
• Treat this as an estimate; calipers, DEXA scans, or bioelectrical impedance scales are generally more precise if you need clinical-grade accuracy.
• Track the trend over weeks or months rather than reacting to any single measurement.

Frequently asked questions

It's reasonably accurate for population averages but less precise for any one individual than lab methods like DEXA scanning — good for tracking trends, less reliable for a single precise number.

Related tools

BMI Calculator

Ideal Weight Calculator

Calorie Calculator

Sources

Tomczak et al. — Comparing Alternate Percent Body Fat Estimation Techniques for U.S. Navy/Marine Corps Body Composition Assessment (accuracy discussion of the Hodgdon-Beckett method) — accessed 2026-08-19

Disclaimer

Educational estimate, not medical advice. Consult a qualified clinician before making health decisions.