Not medical advice.These estimates are for general informational use only and aren't a substitute for professional medical advice, diagnosis, or treatment. Consult a qualified healthcare provider before changing your diet, exercise, or medication.

The US Navy circumference method

This tool uses the US Navy body-fat equation, a tape-measure method developed by Hodgdon and Beckett at the Naval Health Research Center in 1984. Instead of calipers or a lab scan, it estimates body fat from a few girth measurements plus your height, because the circumference of the neck, waist and (for women) hips correlates with subcutaneous fat. The formulas are:

Men: %fat = 495 / (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450

Women: %fat = 495 / (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450

All measurements are in centimetres internally; if you enter inches we convert first. That is why a waist measurement larger than your neck is required (and waist + hip larger than neck for women) — the logarithm of a non-positive number is undefined, so the calculator pauses and asks you to re-check your tape before computing.

The resulting percentage is placed into a neutral descriptive band (essential, athletes, fitness, average, above average) using the sex-specific reference ranges popularised by the American Council on Exercise. These are descriptive groupings, not targets — there is no single "ideal" number, and healthy people span a wide range.

Waist-to-height ratio (WHtR)

Alongside the Navy estimate we report your waist-to-height ratio — simply your waist circumference divided by your height in the same units. It is an emerging screening standard for central adiposity: the UK's National Institute for Health and Care Excellence (NICE guideline NG246, 2022/2023) advises keeping your waist to less than half your height, so a ratio below 0.5 is generally considered healthy. WHtR needs no equation and no sex adjustment, which makes it a useful, transparent companion to the Navy method.

Your data never leaves your device

Your last measurements are saved only in this browser (using localStorage) so the form is ready next time. Nothing is uploaded, there is no account, and no measurement is shared with anyone — including us.

Frequently asked questions

How accurate is the US Navy body-fat estimate?

For most people it lands within roughly 3–4 percentage points of a DEXA or hydrostatic measurement, which is good for a method that needs only a tape measure. Accuracy is best near the population averages the formula was fitted on and drifts at the extremes — very lean, very muscular, or very high body-fat individuals. Treat the number as an estimate and a way to track change over time, not a precise reading.

Why does measurement technique matter so much?

Because the method is built from circumferences, small tape errors move the result noticeably. Use a flexible tape held snug but not compressing the skin, keep it level all the way around, measure on bare skin at the same time of day, and take the waist at the navel and the neck just below the larynx. Measuring the same way each time matters more than getting a "perfect" absolute number.

What are the limitations of this method?

It infers fat from girth, so it cannot distinguish fat from muscle or account for where you carry fat beyond these sites, and it is less reliable during rapid weight change or for athletes with unusual proportions. It is a screening estimate, not a diagnosis or a measure of health on its own.

Should I look at body fat or waist-to-height ratio?

Both, as complementary views. The Navy estimate gives a whole-body fat percentage; the waist-to-height ratio focuses on central fat and is quick to track with a single measurement. Watching the trend in either over weeks is more informative than any single reading.