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.

What is the Body Fat % Calculator (US Navy Method)?

Enter waist, neck, and hip circumferences alongside height to estimate body fat percentage using the US Navy circumference formula, the tape-measure method used in military fitness assessments for men and women. It runs free in your browser on Gera Tools, with nothing uploaded.

Body Fat % Calculator (US Navy Method)

Name: Body Fat % Calculator (US Navy Method)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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 and a height measurement. It powers the body-fat standards used in military fitness programs and is a practical, repeatable way for athletes and coaches to track body composition changes without lab equipment.

How the equations work

The method uses logarithmic regression equations, derived from comparing circumference measurements to reference body-composition data. The logarithmic form was chosen because body fat does not scale linearly with circumference size.

For men:

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

For women (hip measurement added because women carry more peripheral fat):

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

All measurements are in centimetres and the logs are base-10. The denominator estimates body density using the circumference proxy, and the Siri formula (495/density) − 450 converts density to fat percentage. If you enter body weight, the tool derives fat mass and lean mass from the percentage.

Where to measure

Measurement site accuracy is critical — a 1 cm error at the waist can shift body-fat estimates by 1–2 percentage points:

Neck: just below the larynx (Adam’s apple), perpendicular to the spine. Pull the tape snug but not tight.
Waist (men): at the navel, horizontal.
Waist (women): at the narrowest point, usually slightly above the navel.
Hip (women only): at the widest point around the hips and buttocks, horizontal.

Measure on bare skin, not over clothing. Take two or three readings and use the average.

Worked example

For a man who is 180 cm tall, 90 cm waist, 38 cm neck:

log10(90 − 38) = log10(52) ≈ 1.716
log10(180)       ≈ 2.255

body density = 1.0324 − (0.19077 × 1.716) + (0.15456 × 2.255)
             = 1.0324 − 0.3273 + 0.3485 ≈ 1.0536

BF% = (495 / 1.0536) − 450 ≈ 20%

The result illustrates a typical healthy-to-acceptable range for an adult male. Enter your own numbers to see your estimate.

Accuracy and how to use the result

The US Navy method typically falls within about 3–4 percentage points of a reference DEXA scan for most people, though it can underestimate body fat at higher ranges and for individuals with unusual fat distribution patterns. It is far less accurate than DEXA, hydrostatic weighing, or Bod Pod measurement, but those require lab visits costing £50–200+.

The real value of this method is tracking change over time, not the absolute number. If your waist shrinks by 3 cm over 8 weeks while your neck stays the same, the formula will show a drop in estimated body fat — and that trend is meaningful even if the absolute percentage is off by a few points.

For consistent tracking:

Measure at the same time of day (morning, before eating)
Use the same posture and tape tension each time
Record all raw measurements, not just the percentage