How to Calculate the Area of a Circle

In mathematical language, the area of a circle is , however the workings of this may not be immediately apparent. These simple steps will walk you through the process.

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Steps

1- Find “r”. “r” is the radius of the circle. The radius is half the diameter, and the diameter is the width of the circle at its widest point. Should you be trying to calculate the area of a circular object, move a ruler or tape measure from the bottom of the object to the top until you find the widest possible measurement. Try a multitude of angles to be sure, but once you have this figure in centimetres, half it to get the radius.

2- Square the radius. This will give you r². To do this, multiply the radius by itself. i.e. 5.6cm x 5.6cm. This will give you a figure with units cm² i.e. 31.36cm².

3- Multiply by π. π, or pi, is an infinite number i.e. it has a never ending number of decimal places. In general it is rounded up to 3.14, however many exam questions will prefer you to use the π function on a calculator, or to simply leave your answer as π_cm², or, as in the example provided in step 2: π31.36cm². Should you be required to progress to a final answer, you will have a figure of _cm², or, as in the example above, 98.47cm² (to 2 decimal places).

Tips

Read the question! Know how the examiner wishes to have the answer presented and present it accordingly!

Be careful with units. If you are trying to find the area of something as part of a larger question or calculation, make sure that you are using comparable units that will produce a final answer with real life meaning i.e. if you are trying to find the volume of a drum, you cannot multiply an area that was measured in centimetres with the length of the drum that was measured in feet. Similarly, you cannot multiply an area that was measured in centimetres with a length that was measured in metres as this will result in a figure several orders of magnitude out.