The uselessness of donut charts

Donut charts are not good at communicating. They look cool but are just as useless as pie charts. A donut is not just a pie chart with a hole; it’s a distorted stacked bar biting its tail.

Hard to read
#

In terms of shape, there are some warning signs.

It’s difficult to compare circles. They don’t give an immediate impression of any difference between two almost equal sizes, while the same represented as rectangles is clearly noticeable. The same also goes for size estimation; rectangles give a better impression of halves, thirds, etc.

Round objects are difficult to read when divided into segments, which is the whole point of the donut and pie. Every value means a different shape at a different angle and no standard starting point. While bars only change their length – and position if stacked.

Value ticks or lines are useless. All values start where the previous ends. And since donuts only have percentages, the end of a part doesn’t equal its size. Every segment depends on the display of its value.

While it’s always necessary to have some labelling, donut charts require the users to read the data values to understand. A diagram that requires decryption is a detour to the data. It defeats its purpose of giving a quick summary and providing simplified information at a glance.

Limited data types #

No negatives #

The donut, like the pie, can only display specific positive percentages. They can’t handle negative values. I have seen people try, notice the problem and decide to proceed with positive values instead, which made everything else wrong, but it looked the way they wanted.

Always two #

We always need a minimum of two values. Even if there is only one number, the rest of it will be the opposite. When something is 23 per cent done, it’s also 77 per cent not done.

Only existing percentages #

If the data isn’t percentages already, it doesn’t make sense to have the data as percentages and calculating them to represent them as percentages will not do anyone any service.

No increase or comparisons #

Since we can’t go past 100 per cent, increasing percentages don’t work. A 13 per cent increase in revenue will probably look 87 per cent bad. If you compare one set of numbers with another, you’re also better off with another type because there will be no common reference points.

Layout and code hell #

Circles in a layout can be a fun challenge. Circles featuring unpredictable appendages are not. Donut charts require more code and more space in a layout.

Charts, in general, are problematic in a responsive setting, and they can take up a lot of space depending on the number of values and data. What donut charts can potentially save by cramming everything into them is lost in legibility and extra space spent on labels.

The shape itself is difficult to stack and shrink because it requires a specific size to be legible, and it requires so much extra information and space around since it doesn’t have axis values.

Each label and value must ideally be outside the shape, at a distance where it can follow its shape’s size and position. At the same time, it needs to not get in the way of the other values, no matter their shape and placement. Multiple small values next to each other are a potential headache for developers and users.

We also need different colours. While that’s true for many charts, bars side by side can have the same colour, while things that are stacked or overlapped need to contrast each other.

Potential donut chart purposes #

• Filling pages. A typical paper-based problem; on the web, we usually want the opposite. But other charts can do this also; some are just better at communicating, and they can scale down.
• Be pretty and colourful. Donut charts are good at getting attention. It might lead people to read the data. Luckily, we can also achieve that with chart types featuring more tangible shapes.
• Donut charts are somewhat successfully at displaying progress between 0 and 100.

While almost useless from the start, the donut chart’s positive and negative properties worsen with every added value.