What a donut chart is
A donut chart is a variant of the pie chart with the center removed, leaving a ring of segments. Like a pie chart, each segment's arc length (and angle) is proportional to its share of the whole, so the chart represents parts of a single total that sums to 100 percent.
The hollow center is the defining feature. It is often used to display a headline figure, such as the total value or a key percentage, turning the empty space into useful real estate that a standard pie chart wastes.
Strengths and limitations
Some argue the ring shape is easier to read than a full pie because the eye can judge arc length along the ring rather than relying on the harder task of comparing central angles. The format works best with a small number of categories that differ clearly in size.
Like all circular part-to-whole charts, donut charts become hard to read with many slices or slices of similar size, where a bar chart conveys precise comparisons better. They are most effective for showing one or two dominant proportions at a glance.