What Is a Sankey Diagram? A Visual Guide to Flow Data

If you’ve ever looked at a chart and thought, “I wish I could see where everything goes,” you’re thinking of a Sankey diagram.

Sankey diagrams are flow visualizations. They show how quantities move from one stage to another, with the width of each band proportional to the amount flowing through it. The thicker the band, the bigger the flow.

Where Did Sankey Diagrams Come From?

The format is named after Captain Matthew Sankey, an Irish engineer who used it in 1898 to show the energy efficiency of a steam engine. But the most famous early example is Charles Minard’s 1869 map of Napoleon’s catastrophic march to Moscow — often called the best statistical graphic ever drawn.

Today, Sankey diagrams are used everywhere from energy policy reports to Google Analytics.

When Should You Use a Sankey Diagram?

Sankey diagrams shine when your data has a flow structure — things moving from one category to another. Common use cases include:

• Contact center call flows — Where do calls go after the IVR? How many escalate? How many resolve at tier 1?
• Website user journeys — Landing page to signup to checkout to churn
• Budget allocation — Revenue sources flowing into department spending
• Energy flows — Generation to transmission to consumption
• Supply chain logistics — Raw materials to factories to distribution to retail

The key question is: does my data have sources, destinations, and quantities? If yes, a Sankey diagram will probably reveal patterns you can’t see in a table.

How to Read a Sankey Diagram

Reading a Sankey diagram is intuitive once you know what to look for:

1. Nodes are the vertical blocks — they represent categories or stages
2. Links are the colored bands connecting nodes — they represent flows
3. Width encodes quantity — wider bands mean more volume
4. Color usually indicates the source category, making it easy to trace where things originated

The left side typically shows inputs or sources. The right side shows outputs or destinations. Your eye naturally follows the flow left to right.

What Makes a Good Sankey Diagram?

Not all Sankey diagrams are created equal. The best ones:

• Limit the number of nodes — More than 15-20 nodes gets hard to read
• Use clear, descriptive labels — “Tier 1 Resolution” beats “T1R”
• Choose a meaningful color palette — Colors should help distinguish sources, not just look pretty
• Size the canvas appropriately — Give the flows room to breathe

Creating Your First Sankey Diagram

With Sankey Flow Studio, you can create a Sankey diagram in under a minute:

1. Paste your data in a simple Source [Value] Target format
2. Customize colors, fonts, labels, and layout
3. Export as SVG or PNG for presentations and reports

No coding required. No complex software to install. Just paste your data and see the flow.

Here’s an example of what the input data looks like:

Inbound Calls [5000] IVR Menu
IVR Menu [3200] Tier 1 Support
IVR Menu [1200] Self-Service
IVR Menu [600] Abandoned
Tier 1 Support [2400] Resolved
Tier 1 Support [800] Escalated to Tier 2
Escalated to Tier 2 [600] Resolved
Escalated to Tier 2 [200] Escalated to Manager

That’s it. Paste it in, and you’ve got a professional Sankey diagram showing your call center’s entire flow structure.

Why Contact Center Teams Love Sankey Diagrams

If you run a contact center, you already have the data — call volumes, routing paths, resolution rates, escalation chains. But spreadsheets hide the story.

A Sankey diagram makes the story visible:

• Spot bottlenecks — See exactly where calls pile up
• Track escalation paths — Understand which issues can’t be resolved at tier 1
• Measure self-service effectiveness — How many customers resolve without an agent?
• Communicate with stakeholders — One diagram replaces a 10-slide deck

“We replaced our monthly 15-page call routing report with a single Sankey diagram. Leadership finally understood where the bottlenecks were.”

Get Started

Ready to turn your flow data into something visual? Sign up for Sankey Flow Studio — it’s free to start, and you can create your first diagram in under 60 seconds.