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Body Fat Calculator

Estimate your body-fat percentage from tape-measure numbers in seconds — no calipers, scales, or gym visit needed.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Select your sex, then measure your neck, waist (and hip if female) and height with a flexible tape in centimetres.
  2. 2.Type each measurement into its field — the estimate updates instantly as you type.
  3. 3.Read your estimated body-fat percentage and fitness band, and re-measure for a more reliable average.

About Body Fat Calculator

The Body Fat Calculator estimates your body-fat percentage using the U.S. Navy circumference method, a tape-measure formula developed by the Naval Health Research Center that needs only a few body measurements instead of calipers, hydrostatic weighing, or a DEXA scan. Enter your height, neck, and waist (women also add hip) in centimetres, and the tool returns your estimated body-fat percentage to one decimal place, plus a simple fitness-band label. Everything is computed locally in your browser — nothing you type is uploaded or stored, so you can measure privately at home with just a soft tape measure.

The method works because certain circumferences correlate with the ratio of fat to lean mass across large populations. For men, the waist-minus-neck measurement captures abdominal fat; for women, the waist-plus-hip-minus-neck measurement reflects both abdominal and lower-body fat, which is why the two sexes use different equations. Those values are fed through a base-10 logarithmic equation and scaled to a percentage. Because it relies on a fixed statistical model rather than direct tissue measurement, the Navy method is best treated as a quick screening estimate: it typically lands within a few percentage points of gold-standard techniques for average adults, but it can be less accurate for very lean, very muscular, or older individuals, and it does not account for exactly where fat sits on any specific person.

To get the most reliable number, measure with a flexible tape on bare skin, keep the tape snug but not compressing, and stay relaxed rather than sucking in or flexing. Measure the neck just below the larynx with the tape sloping slightly downward at the front, the waist at the navel for men and at the narrowest point for women, and the hips at their widest point around the buttocks. Keep the tape level and parallel to the floor, and read it after a normal exhale. Taking each measurement two or three times and averaging the readings reduces error, since a single centimetre off can shift the final result by roughly a percentage point.

Body-fat percentage is a more informative body-composition signal than weight or BMI alone, because two people at the same weight can carry very different amounts of fat and muscle, and BMI cannot tell the two apart. A rising body-fat estimate alongside steady weight can flag muscle loss, while a falling estimate during resistance training often signals recomposition. For that reason, use this estimate to track trends over weeks and months from consistent, same-conditions measurements rather than obsessing over a single reading or comparing your number to someone else's. Morning measurements before eating tend to be the most repeatable.

This is a wellness and fitness tool, not a diagnostic device — for a clinical assessment of body composition, cardiovascular risk, or any health condition, consult a qualified healthcare professional who can use validated measurement equipment and interpret the results in the context of your full medical picture.

Methodology & sources

Body-fat percentage is estimated with the U.S. Navy circumference method (Hodgdon–Beckett equations from the Naval Health Research Center), using base-10 logarithms of neck, waist, height (and hip for women) in centimetres. For men: 495 / (1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height)) − 450. For women: 495 / (1.29579 − 0.35004·log10(waist + hip − neck) + 0.22100·log10(height)) − 450. It assumes accurate tape measurements on bare skin and is a statistical estimate calibrated on population averages, so accuracy varies for very lean, very muscular, or older individuals. This is a fitness screening estimate, not a clinical body-composition measurement and not medical advice — consult a qualified healthcare professional for diagnosis or health decisions.

Frequently asked questions

How accurate is the U.S. Navy body-fat method?
For average adults it usually falls within about 3–4 percentage points of gold-standard methods like DEXA or hydrostatic weighing. It is less accurate for very lean, very muscular, or older people, so treat it as a screening estimate rather than a precise measurement.
Why do women need to enter a hip measurement but men do not?
The Navy formula uses different equations by sex. The men's equation relies on waist minus neck, while the women's equation adds hip circumference because female body-fat distribution makes the hip measurement statistically important for an accurate estimate.
Where exactly should I measure my neck, waist, and hips?
Measure the neck just below the larynx, the waist at the navel for men and at the narrowest point for women, and the hips at their widest point. Keep the tape snug but not compressing the skin, and measure on bare skin while relaxed for the most consistent numbers.

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