Sankey diagram best practices: 9 rules that make yours readable

Sankey diagrams fail in predictable ways. They get too many nodes, the labels collide, colours are picked for prettiness instead of meaning, and the reader gives up. These rules fix most of it.

1. Twelve nodes is a good ceiling

Above roughly a dozen nodes, ribbons start overlapping and the eye can no longer follow a single path. Group the long tail into an Other node. You lose granularity that nobody was reading anyway and gain a chart that survives being seen on a phone.

2. Sort every column by size

Put the biggest flow at the top of each column and descend from there. Consistent ordering removes crossings, and crossings are what make a Sankey look like spaghetti.

3. Use colour as a verdict

Three colours is usually enough: one for good outcomes, one for losses, one neutral for the trunk. A rainbow palette makes the chart look designed and read worse, because the reader has to learn a legend before understanding anything.

4. Label on the node, not in a legend

Legends force the eye to bounce. Put the name and the value next to the node itself, and put percentage change on a second line if you have last period's numbers.

5. Round the numbers

A Sankey is a proportion chart, not a ledger. $3.8M reads instantly; $3,812,447.19 does not, and nobody is going to reconcile it from a picture.

• 6. Keep the trunk horizontal — a diagonal main flow is harder to follow.
• 7. Never let a ribbon disappear behind a node; nudge the node instead.
• 8. Give the chart a title that states the conclusion, not the dataset.
• 9. Export at 2x. Sankey labels are small by nature and blur first.

None of these rules are about taste. Each one removes a specific way the reader can get lost, which is the entire job of the format.