Let's step back for a moment: are you committed to using a pie chart? Prominent information design guru Edward R. Tufte speaks harshly of them in The Visual Display of Quantitative Information:
Tables are clearly the best way to show exact numerical values, although the entries can also be arranged in semi-graphical form. Tables are preferable to graphics for many small data sets. A table is nearly always better than a dumb pie chart; the only worse design than a pie chart is several of them, for then the viewer is asked to compare quantities located in spatial disarray both within and between pies.
I'm surprised that Tufte does not also remark that a 3-D pie chart is worse than a 2-D pie chart as a 3-D pie chart uses three dimensions to represent one number rather than two dimensions to represent one number, which is bad enough. Comparing areas (2-D) is hard; comparing volumes (3-D) is harder.
You can find some gainsayers noting that one redeeming quality of a pie chart is that the numbers sum to a whole. And I add that a circular display may fit well in a small viewport such as a smartphone, though some tables may not.