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Body fat calculator

Estimate your body fat percentage with the US Navy method using height, waist and neck (plus hip for women).

Required fields are marked with an asterisk (*).

Sex
The Navy method uses a different constant by sex.
Your height in centimetres.
Measure around the waist near the navel level, with a tape that is level and not pulled tight, over bare skin.
Measure around the neck just below the larynx, with the tape touching and not tight.

Body fat percentage tells you more about your body composition than weight alone. This calculator estimates it with the US Navy method using only body circumferences: height, waist and neck, plus hip for women. The result is an estimate that depends on the accuracy of your measurements.

Formula

For men: body density = 1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height); for women: = 1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height); then body fat % = 495 ÷ density − 450.

When is this useful?

Use this calculator to track changes in your body composition over time using the same measurement technique, to estimate the direction of the percentage instead of relying on weight alone.

Worked example

Example using the calculator’s values: male, height 180 cm, waist 90 cm and neck 40 cm.
Body fat percentage is about 18.4%.

Assumptions

  • The US Navy circumference method is used as an estimate.
  • The result depends on measurement accuracy: a touching, not tight, level tape.
  • The equation differs between men and women.
  • The estimate is general and may differ from more precise methods such as hydrostatic weighing or imaging.
  • Results are indicative and are not a medical diagnosis.

Common mistakes

  • Measuring over clothing or with a pulled-tight tape, which distorts the result.
  • Entering measurements in inches where centimetres are expected.
  • Forgetting to enter the hip circumference for women.
  • Measuring at different times of day, so results vary without anything real changing.

Frequently asked questions

How accurate is the Navy method?

It is a reasonable estimate for many people within a few percentage points, while more precise methods such as hydrostatic weighing or imaging scans give more accurate results.

Why is the hip measured only for women?

Because fat distribution differs between sexes, and the female equation includes the hip circumference to reflect fat accumulation in that area.

How do I take a correct measurement?

Measure in the morning and the same way each time: a touching, not tight, level tape directly on the skin, without sucking in your stomach.

Methodology and review

The calculator applies the US Navy equations, which estimate body density from circumference measurements and convert it to a body fat percentage, with different constants for men and women.

Results are estimates for awareness purposes only and do not constitute a diagnosis or medical advice. Consult a professional about any health concerns.

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