Body Fat Calculator

Estimate body fat using the U.S. Navy circumference method

Unit system

Sex

Male Female

Height

Waist circumference

Neck circumference

How the calculator estimates your body fat

The calculator uses the U.S. Navy circumference method. From your height and a few circumferences it estimates how much of your weight is fat. For men it uses waist and neck; for women it adds the hip measurement. All you need is a tape measure — no device and no scale.

Measuring correctly

Measure your waist horizontally at navel level, your neck just below the larynx, and your hips at the widest point of the buttocks. Stand relaxed, breathe out normally and don't pull your stomach in. Keep the tape flat against the skin without digging in. Measure each circumference twice and take the average so small reading errors cancel out.

How to use the calculator

First choose your unit system and sex. Then enter your height, waist and neck; if you are a woman, add your hip measurement. Clicking “Calculate body fat” shows the estimated percentage and assigns it to a category. If a value is missing or the waist is smaller than the neck, the calculator tells you instead of returning a nonsensical result.

A worked example

Say you are male, 180 cm tall, with a 90 cm waist and a 40 cm neck. The method combines the difference between waist and neck with your height and estimates roughly 18 % body fat — that sits in the average range. A smaller waist lowers the estimate, a larger one raises it. For women, the hip measurement feeds into the same calculation.

Reference ranges

This breakdown is only a rough guide and is no substitute for a medical assessment. It matches the categories the calculator assigns to your result:

Category	Men	Women
Essential fat	under 6%	under 14%
Athletic	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
Elevated	25–31%	32–39%
High	32% and up	40% and up

Limits of the estimate

Because it uses only circumferences, the formula can't tell muscle from fat and ignores bone structure and fat distribution. Hydration, meals and tape tension make the value fluctuate from day to day. For very muscular, very lean or heavily overweight people, and for unusual body types, the estimate can be well off. More accurate but more demanding options are DEXA, hydrostatic weighing or the Bod Pod. Treat the result as a reference point and watch the trend over weeks rather than a single measurement.

Frequently Asked Questions

Where do I take the measurements?

Measure your waist horizontally at navel level, your neck just below the larynx, and — for women — your hips at the widest point of the buttocks. Breathe out normally and don't pull your stomach in.

How tight should the tape be?

Keep the tape flat against the skin without digging in, and don't let it sag. Hold it level all the way around and measure each circumference twice — a third time if the readings differ noticeably — then take the average.

Which formula does the calculator use?

It uses the U.S. Navy circumference method. For men it takes height, waist and neck; for women it adds the hip measurement. The circumferences are combined on a logarithmic scale, and the estimate is typically within about ±3–4 percentage points of a lab reference.

Why does the value change from day to day?

Hydration, meals, salt and the time of day shift your circumferences by a few millimetres, and that alone moves the estimate. Measure in the morning, before eating, and always under the same conditions if you want to compare values over time.

How does the estimate differ from DEXA or calipers?

DEXA, hydrostatic weighing and the Bod Pod are considered more accurate but are costly and hard to access. Caliper readings measure skinfolds directly but depend heavily on technique. The circumference method needs only a tape measure, making it a practical compromise for home use.

Who is the formula less suitable for?

Because it uses only circumferences, the formula can't tell muscle from fat. It can be off for very muscular, very lean or heavily overweight people and for unusual body types. Treat the result as a rough guide and watch the trend rather than a single reading.