Parts of a whole, and only that
A pie chart shows how one total divides. Every slice is a share of 100%, the angles sum to 360 degrees, and the chart works when the whole is meaningful: a budget, a vote, a market. It fails, often hilariously, at everything else. If your numbers do not add up to a total that means something, this is the wrong chart, whatever the presentation software suggests.
The $3,000 monthly budget: rent 1,100 (36.7%), savings 500 (16.7%), groceries 400 (13.3%), debt 300 (10.0%), transport 250 (8.3%), fun money 190 (6.3%), utilities 150 (5.0%), phone 60 (2.0%), subscriptions 50 (1.7%). The pie makes the strategic fact visible at a glance: housing alone out-eats groceries, transport and fun money combined, which is where budget advice for this household has to start.
Angles are harder to judge than lengths
Readers rank bar lengths precisely and slice angles poorly, especially slices that do not start at the top and especially in the 15 to 30% range where neighbours look alike. So keep pies to a handful of slices, label every slice with its percentage (the tool does), and start the largest slice at twelve o'clock. For comparisons across two wholes (this year vs last), side-by-side bars beat side-by-side pies every time.
The exploding, tilted, 3D pie: slices pulled out, perspective warping the far side smaller. It decorates at the cost of the only thing a chart owes you, accurate comparison. Flat, labelled, few slices: that is the whole craft here.
When the pie is the right call
One dominant share to dramatize (rent at 36.7%), a two-way split near a decision threshold, or a composition your audience already thinks in percentages. For trends, rankings and close comparisons, choose the bar chart and do not look back.
Frequently asked questions
How is a slice angle calculated?
Share times 360 degrees. Rent at 36.7 percent of the total takes 0.367 x 360 = 132 degrees of the circle. The tool's table shows every slice's angle and share.
How many slices can a pie chart have?
Five to seven, with labels. Beyond that, slices become slivers that cannot be compared or even read; switch to a bar chart or group the tail as Other.
Why do people say pie charts are bad?
Angles are hard to compare precisely, and pies get abused for data that are not parts of a whole. For a simple composition with few slices, honestly labelled, they are fine and familiar.
Can values include zero or negative numbers?
No. A slice needs a positive share of a positive total. Zero rows are dropped by the tool; negative values mean the data are not a composition at all.