Body composition · Free tool

Body fat calculator

Body fat calculator estimates body fat percentage from height and tape measurements using legacy Navy-style circumference equations.

A fit, athletic man calmly uses a flexible tape measure at his waist in a bright, tranquil bedroom, exuding self-assurance.

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Your estimate

Estimated body fat · legacy tape equation

18.46 %

A circumference-based estimate with individual measurement error. This is not a current military compliance assessment or a direct measurement of body composition.

How to use this Body fat calculator

  1. Choose the male or female equation and matching units.
  2. Measure height without shoes. Keep the measuring tape snug without compressing the skin.
  3. Measure the neck below the larynx. For the male equation use abdomen at the navel; for the female equation use the natural waist and hip at the widest point.
  4. Enter the measurements and select Calculate. Repeat measurements consistently when comparing trends.

The formula and method

The implemented male equation is body fat % = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76. The female equation is 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All measurements inside these equations are in inches.

Metric inputs are converted from centimetres to inches before the logarithms are evaluated. These direct percentage equations are a legacy circumference approach; they are not the same numerical expression as the density-and-Siri form sometimes published for the method.

The input measurements must produce a positive logarithm argument and a usable percentage. The tool reports an error when a combination produces a non-positive or implausible result rather than silently clamping the result.

Worked example

For a male equation with height 180 cm, abdomen 90 cm and neck 40 cm: convert to inches, then use 86.010 × log10(50 ÷ 2.54) − 70.041 × log10(180 ÷ 2.54) + 36.76. The estimate is about 18.46% body fat.

Understanding the estimate

  • This is a legacy circumference estimate, not a current military compliance assessment.
  • Measurement site, tape tension and individual body shape can materially affect the estimate.
  • It does not directly measure body composition or identify where fat is stored.

Frequently asked questions

Why does the female equation need a hip measurement?

The two historical regression equations use different measurement combinations. The female equation includes hip circumference; the male equation does not.

Why is my result rejected?

Check the units and measurement sites. The equation requires a positive circumference difference and a plausible output; some body shapes are outside its useful range.

Is this the same as a laboratory body-composition measurement?

No. It estimates a percentage from tape measurements and a historical model. Individual error can be meaningful.

Sources and further reading