This page discusses how to make a successful pie chart, including:
Pie charts can only ever be used to display categories that represent parts of a whole. In other words, the chart as a whole represents a "something", and the pieces of the pie are all the different components that add up to make the "something."
Strive for clarity: The title of your chart should be descriptive and tell the viewer what to look for. Also consider how best to identify the different slices of the pie. Using a legend makes your audience have to look back and forth between the slices and the legend; instead of including a legend, can you add text next to or directly on top of each slice?
Make it a clock: Sort your pie slices so that the largest slice starts at 12 o'clock and extends clockwise. As you go clockwise around the chart, each subsequent slice should be smaller. (To make this happen you may have to sort the data itself, largest to smallest, before creating the chart.) Setting up your pie chart this way will make it a lot easier and faster for audiences to read.
Pie charts get a bad rap because they are so often abused. Don't make these mistakes!
Below is a bad pie chart.
The chart is 3D, there are too many slices, and the slices aren't ordered in a way that makes their sizes easier to distinguish. Don't make a pie chart like this. Its only saving grace is that the slices add up to 100%.
Color: One important consideration for accessibility is the use of color. There are several different types of color-blindness, which can affect how well your audience reads your chart. The most common is red-green color-blindness, which means that red and green look very similar. As much as you may want to use green to mean something positive and red to mean something negative, you should pick a different pair of colors instead. The websites ColorBrewer, Contrast-A, and Viz Palette are great tools for identifying colors that work well together and also work for color-blind audiences. You can also check your finished product against a color blindness simulator. You may also want to test how your chart looks in black and white, either by printing it out or using your chart creation tool to transform the colors to grayscale.
Text: It's also important to ensure that any text on your chart is easy to read, which is affected by both the size of the text and the choice of font. Try to avoid "pretty" fonts; it's best to use something sans serif like Ariel or Calibri. When designing your chart, try to keep all text horizontal (nobody wants to have to tilt their head to read). Make sure your chart title and any labels are descriptive and clear.
Embedding an image: If you are embedding the chart as an image in a document or online, you should also include an "alt" tag that describes what the chart shows. If you are able to share the data behind the chart, it is also recommended to provide a descriptive link to the data near the chart image.