Single-dimensional measurement units like centimeters can be converted into two-dimensional units like square centimeters through common geometric shapes' area formulas. A circle's diameter, one of its defining and longest linear measurements, is a line segment that extends from one point on its circumference, through the circle's center and to another point on its circumference. With the diameter, you can find a circle's area with the equation 1/4 * diameter^2 * pi, where pi is a math constant that approximately equals 3.142, and convert measurements in centimeters to square centimeters.

- Measuring tape
- Calculator
If the diameter is given in units other than centimeters, then convert the measurement with a conversion program (see Resources).

Measure the diameter in centimeters. For this example, let the diameter measure 10 cm.

Multiply the diameter's length to itself to square it — 10 cm multiplied by 10 cm results in 100 cm^2.

Multiply the squared diameter by pi — 100 cm^2 multiplied by pi equals approximately 314.2 cm^2.

Divide the product from the last step by 4 to calculate the circle's area — 314.2 cm^2 divided by 4 equals 78.55 cm^2.