Home › Fitness & Health › Body Fat Calculator
FREE · NO SIGN-UP · TRANSPARENT FORMULAS

Body Fat Calculator

Explore a historical circumference-based estimate with US or metric measurements.

Your numbers

Make it your own
Updates as you type
Estimated body fat
17.5131%

Calculated from your inputs · rounded for display

Measurement systemInches
EquationMale circumference equation

Historical US Navy circumference estimate for adults, not a direct measurement, diagnosis or current military eligibility test. Male waist: abdomen at navel; female waist: natural waist; hips: widest point; neck: below larynx. Measurement technique and body shape affect accuracy. Not for pregnancy.

Your calculation, step by step

No black boxes
  1. Convert measurements to inches before applying the coefficients.
  2. Circumference combination = 19 in; height = 70 in.
  3. Body fat % = 86.010 log10(waist − neck) − 70.041 log10(height) + 36.76.
  4. Estimated body fat = 17.513085%.

How to use this calculator

  1. Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
  2. Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
  3. Copy, share, save, or download your result. Saved inputs stay on this device.

How the calculation works

Male %BF = 86.010 log10(waist − neck) − 70.041 log10(height) + 36.76; use inches

The historical Navy equations relate height and specific body circumferences to estimated body-fat percentage. Male abdomen is measured at the navel; female waist is measured at the natural waist and hips at the widest point. Values are converted to inches internally. Technique and body shape can materially affect accuracy.

A worked example

For the male equation at 70 inches tall, waist 34 inches and neck 15 inches, the circumference difference is 19 inches; the displayed logarithmic equation gives approximately 17.5131%.

Reading your result

Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.

Frequently asked questions

Does this measure body fat directly?

No. It is an indirect population equation, not a diagnosis.

Is this a current military qualification tool?

No. It does not determine military eligibility or apply current policy.

Sources & methodology

US Army: historical circumference equations (unrounded arithmetic here) ↗

Formula review: October 24, 2026. Read our methodology.