An Excel user asked how to produce pie charts of different sizes, so that the total of the wedges comprising each pie dictates its size. The idea behind the different sized pies is to provide a qualitative display of the whole pies and the individual wedges.
I pointed out the generally poor ability to judge areas, and proposed a bar chart alternative that provides not only a qualitative3 display, but also a quantitative display.
The user posted the following sample data showing the hourly costs of operation of three conveyors, broken down into four constituent cost elements.
The user envisioned a display of pie charts similar to the following. Conveyor 2 has the greatest costs. Conveyor 1 has the lowest costs, only 35% that of Conveyor 2, and Conveyor 3 has nearly the same costs, 43% those of Conveyor 1. If we make the area proportional to cost, the diameter of the pies will be proportional to the square root of cost, so Conveyors 1 and 3 have pies with diameters 59% and 65% as large as that of Conveyor 2.
You can see that Conveyor 2 is the most expensive to operate, and you may get a sense that conveyor 1 is the cheapest. But it is at best a qualitative view. You cannot easily compare the magnitudes of the operating costs of the conveyors. You can roughly judge that Power is a somewhat larger proportion of Conveyor 2’s operating costs, but you cannot compare the relative costs of operator and parts.
The ineffective comparisons offered by the pie charts can be fixed by using a single bar chart. In fact, a simple clustered bar chart is sufficient, with one cluster per conveyor showing the total and constituent costs of operation. We can readily compare the total costs of operation, and we can see that the costs of operator and parts make up only a tiny and nearly invariant portion of the total.
Some labeling of the bars can help if we need to show precise values or percentages. The total bar labels below show simply the corresponding values, while the percentages of the other bars have been computed in the worksheet, and added to the bars using Rob Bovey’s free and indispensable Chart Labeler add-in.