How accurate is the US Navy method?

It is typically within about 3-4% of a DEXA or hydrostatic scan for most people. It is far cheaper and repeatable, but it estimates from circumferences rather than measuring fat directly, so use it for tracking trends rather than as a clinical reading.

Where exactly do I measure?

Measure the neck just below the larynx, the waist at the narrowest point for women or at the navel for men, and the hips at the widest point. Keep the tape snug and level, and measure on bare skin for consistency.

Why does the formula need height?

Circumferences alone do not indicate body fat without a frame reference. Height anchors the regression equation so the same waist measurement maps to different body fat values for a tall versus short person.

Why is the women's formula different?

Women carry more essential fat and store it differently, so the Navy uses a separate equation that adds hip circumference. Using the male formula for a woman would significantly underestimate her body fat.

Can I use centimetres and kilograms?

Yes. This tool runs the metric version of the equations, so enter all circumferences and height in centimetres. The math uses base-10 logarithms exactly as published by the US Navy.

Body Fat % Calculator (US Navy Method)

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A tape measure body-fat estimate

The US Navy developed this circumference-based method so body composition could be assessed with nothing but a tape measure. It powers the body-fat standards in many military fitness programs and is a practical, repeatable way for athletes to track changes without lab equipment.

How it works

The method uses logarithmic regression equations derived from circumference measurements and height. For men:

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

For women, hip circumference is added:

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

All measurements are in centimetres and the logs are base-10. The denominator estimates body density, and the Siri-style conversion turns density into a fat percentage. From that percentage the tool derives fat mass and lean mass if you supply body weight.

Tips and example

A man who is 180 cm tall with a 90 cm waist and 38 cm neck gets log10(90 − 38) = log10(52) feeding the equation, landing around 17-18% body fat. Small tape errors move the result, so measure two or three times and average.

For meaningful tracking, always measure at the same time of day, in the same posture, with the tape at the same tension. The absolute number matters less than the direction of change over weeks.