Pie charts are used to show the percentage distribution of parts of a total. Because it is difficult to accurately compare segments of a pie, you should not have more than six categories in your pie chart. Additionally, label the categories in the segments of the pie to aid in comparison. Finally, avoid comparing data across two or more pies. Sections in pie charts are not easy to compare and hence to show two pies and ask readers to compare is not a good idea if there are no great differences.