Pie chart vs donut vs treemap: showing parts of a whole

Budget breakdowns, market share, where the ad spend went — sooner or later every report needs a parts-of-a-whole chart, and three candidates apply for the job. The pie, the donut and the treemap all show how a total splits. They are not interchangeable, and the choice is simpler than the endless pie-chart discourse suggests.

The pie: one dominant slice, instantly

Humans read angles poorly but read "more than half" perfectly. A pie shines when the story is dominance: one slice at 60% next to a scatter of small ones needs no labels to land. It collapses when slices are similar — nobody can rank 23% against 19% and 21% by eye.

The donut: a pie with a headline

Structurally a donut is a pie, and the same six-slice discipline applies. The hole is the feature: it gives you a place to print the total or the key percentage, which is why dashboards love it. If you were not going to put a number in the middle, you just wanted a pie.

The treemap: when the parts multiply

Past six categories, rectangles beat wedges. A treemap keeps twenty shares comparable because areas sit side by side, labels fit inside the tiles, and small categories stay visible instead of vanishing into slivers. It is the right default for portfolios, app storage, expense categories — any whole with a long tail.

The rule of six, and two honest warnings

The working rule: six slices or fewer with one clear leader, take the pie or donut; more than six, or similar-sized parts, take the treemap. Two warnings apply to all three: the parts must genuinely sum to a meaningful whole, and if the real story is how shares changed over time, none of these is your chart — that is a stacked area.

• ≤6 slices, one dominant → pie or donut.
• Need the total or KPI visible → donut, number in the hole.
• More than 6 categories or a long tail → treemap.
• Shares changing over time → stacked area, not a parts-of-a-whole chart at all.

The empirical answer is one chart-type switch away: load your numbers once and flip between pie, donut and treemap from the toolbar until one of them makes the sentence you care about obvious.