Pie Charts

Slices of a whole

A pie chart shows each category as a slice of a circle. The whole circle — all 360^\circ of it — represents the total amount of data. Each category gets a slice, and a bigger slice means a bigger share of the whole.

How wide is a slice? Its angle is the category's share of the total, taken out of 360^\circ:

\text{slice angle} = \frac{\text{frequency}}{\text{total}} \times 360^\circ

For example, if 10 of 20 people chose tea, that slice is \frac{10}{20} \times 360^\circ = 180^\circ — exactly half the circle.

the whole circle is 360^\circ and represents the total;
each slice's angle is \dfrac{\text{frequency}}{\text{total}} \times 360^\circ;
to read a slice back, its frequency is \dfrac{\text{slice angle}}{360^\circ} \times \text{total};
all the slice angles add up to 360^\circ.

Build a pie chart

Twenty people picked a drink: 10 chose tea, 5 chose coffee and 5 chose juice. Step through to draw the three slices, then label each angle.