Body Fat Calculator

What this calculator estimates

Estimate body-fat percentage from tape measurements using circumference equations commonly associated with the US Navy method. Body weight is then used to estimate fat mass and lean mass.

Inputs and calculation method

Choose the equation option and enter height, neck and waist measurements in centimetres. The female equation also uses hip circumference; hip does not enter the male equation. Enter weight in kilograms for the mass outputs. The circumference and height terms are converted to inches internally.

Formula and units

With measurements in inches, the male equation is 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. The female equation is 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. Each centimetre measurement is divided by 2.54 before applying those constants. Fat mass = weight × body fat % ÷ 100; lean mass = weight − fat mass.

How to use it

1. Use a flexible tape, level against the skin without compressing it.
2. For the male equation, measure abdomen at the navel; for the female equation, use natural waist and the widest hip circumference.
3. Enter all lengths in cm and body weight in kg.
4. Calculate using consistent tape placement; invalid circumference combinations cannot produce a meaningful estimate.

Worked example

Using the female equation with height 165 cm, neck 34 cm, waist 75 cm and hips 95 cm gives approximately 26.7% body fat. At 70 kg, that corresponds to 18.7 kg estimated fat mass and 51.3 kg lean mass. A male example at 180 cm, neck 40 cm and abdomen 90 cm gives approximately 18.5%.

How to read the result

These are circumference estimates, not a scan or a direct measure of muscle. Consistent tape placement matters. Do not compare a small change with a result from a different measurement method and assume it represents a real body-composition change.

Common mistakes

• Mixing centimetres and inches.
• Measuring a male abdomen at the narrowest waist rather than the navel.
• Pulling the tape tight or changing tape placement between measurements.

Method limitations

Circumference equations have individual and population error. Lean mass includes water, organs and bone as well as muscle; neither output diagnoses health or establishes an appropriate body-fat target.

Sources and method references

• Published circumference equations with centimetre-to-inch conversion
• US Navy body-fat chart: inch-based height and circumference

Using the estimate

Use centimetres consistently, follow the equation-specific measurement sites and treat small changes cautiously. The method estimates body composition rather than directly measuring it.