Sankey diagram

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A Sankey diagram encodes quantity in the width of each flow, which makes it unusually good at showing where things go missing: budget, traffic, energy, or users falling out of a funnel.

It is the right chart when the question is not how much, but how much went where.

#When to reach for one

  • Funnel analysis, where the drop-off is the finding.

  • Budget and cost allocation across categories.

  • Energy, material or traffic flows through a system.

#How to draw it in Capable

Route

Use when

Mermaid

A compact source and value syntax; the quickest route.

Vega

Full control of colour, ordering and labelling.

#A worked example

A sign-up funnel, with the losses visible:

Sankey diagram

The source, which you can paste into a new diagram and edit:

sankey-beta

Visitors,Started sign-up,4200
Visitors,Left immediately,15800
Started sign-up,Verified email,3100
Started sign-up,Abandoned form,1100
Verified email,Completed onboarding,2400
Verified email,Stalled after verification,700
Completed onboarding,Active after 30 days,1500
Completed onboarding,Churned in first month,900

#A few things that catch people out

  • Flows must balance. If what leaves a node exceeds what entered, the diagram is wrong.

  • Name the loss paths explicitly. "Abandoned form" tells you more than a missing arrow.

  • Keep the number of nodes small; Sankey diagrams get illegible quickly.

Keep the numbers where people can check them.