Pie charts are an almost guaranteed element of most dashboards, but that doesn't make them great ways to Display data. Here are 5 reasons not to use pie charts in your dashboards:
1. They're difficult to visually gauge proportions
Got a category on your pie chart at 7%? Could you spot that it was 7% without a legend or commentary? Didn't think so.
If a chart requires call out commentary to be able to read an actual value, then the chart isn't doing its job particularly well! A simple table or column/bullet chart would show this much better.
2. They're cluttered with any more than a couple of categories
If you are using a pie chart to display any more than a couple of categories you're asking for the chart to be ignored be your audience. Even worse, is your pie chart so bad that the legend is as big as the chart itself, and there's so many colours you can't tell them apart?
If this is the case you should question if a pie chart is really the best way to display your data. A simple bar chart may be a much better solution.
3. They are unable to show trending
If you're using a pie chart to display performance of a specific metric at a point in time, why aren't you showing trending over time? Pie charts cannot do this.
I've seen dashboards with date drop downs and fancy sliders, but ultimately it's never a good way to display a metric over time.
If you only have a couple of categories consider a 100% stacked bar chart, if you have more consider a regular bar chart with a drop-down menu for the category.
4. They one dimensional
This is an obvious one, but you can only display a single point in time value on a pie chart. Yes, you could add filters for other categories and allow the chart to update when used, but what it's often better to track multiple metrics on a single chart as a comparison, or use other charts types to create multidimensional bar charts.
5. They're a waste of valuable space
For a chart that shows no trending, one dimension, one metric, pie charts take up far too much valuable space on any dashboard. Maybe the old fashioned managers still love them, but we'd recommend avoiding pie charts at all costs when designing dashboards in any business scenario.