What Is a Sankey Diagram?

A Sankey diagram is a type of flow diagram where the width of each connection is directly proportional to the quantity it represents. The wider the band, the larger the value. The narrower the band, the smaller the flow.

Named after Irish engineer Captain Matthew Henry Phineas Riall Sankey, who used the format in 1898 to show energy losses in a steam engine, today you’ll find it everywhere from energy efficiency reports to marketing funnel analysis, any time someone needs to show not just how much, but where it all went.
Unlike a bar chart or a pie chart, a Sankey diagram shows movement. It answers not just “how much?” but “where does it go?” making it the right choice any time you need to trace how a quantity splits, merges, or transforms across stages.

How a Sankey Diagram Works

Every Sankey diagram is built from two structural elements:

• Nodes — the rectangular blocks or labels that represent a category, stage, or entity. For example: “Organic Search,” “Homepage,” “Product Page.”
• Links (flows) — the bands connecting the nodes. The width of each link is scaled to the flow it represents. If 10,000 visitors arrived via organic search and 3,000 went to the product page, that link is proportionally narrower than the one showing 6,000 going to the homepage.

Most Sankey diagrams read left to right, moving from source to destination through one or more intermediate stages. The total value entering a node always equals the total value leaving it, which means the chart self-validates and makes inconsistencies visible immediately.

Data for a Sankey is structured as three columns: from, to, and weight. Each row defines one link: where the flow starts, where it ends, and how large it is.

Common Use Cases

Pick the wrong chart for a flow problem, and the insight disappears into rows of numbers. Here are the scenarios where a Sankey earns its place:

Website Traffic & User Paths

Visualize how visitors arrive at your site (organic, paid, direct, social), which pages they land on, and where they go next. A Sankey diagram makes drop-off points and dominant paths immediately visible, something a standard traffic report cannot do.

Marketing & Sales Conversion Funnels

Map the journey from first touch to closed deal. Connect acquisition channels to lead stages to converted revenue, with each band sized by the number of prospects. You can see at a glance which channel converts and where the funnel loses the most volume.

Budget & Cost Allocation

Show how total budget flows from a central source through departments, teams, and line items to final expenditures. You can show how total budget flows from a central source through departments, teams, and line items to final expenditures in a way that tables and pie charts simply can’t. It’s especially useful when the same fund feeds multiple downstream categories.

Customer Journey Visualization

Use a Sankey to trace how your customers move through touchpoints, product categories, or support stages. You’ll see which steps create friction, which paths lead to retention, and exactly where people disengage before completing their journey without having to build a separate report for each question.

Energy & Resource Flow

One of the original use cases: mapping how energy (or any physical resource) enters a system, transforms through stages, and exits as useful output or waste. If you work in operations, manufacturing, or sustainability, this is likely the most precise way to show where losses occur and what drives them.

Sankey Diagram vs. Similar Chart Types

Sankey diagrams are often confused with related visualization types. The differences matter when choosing the right chart for your data:

Chart type	Best for	When to use instead
Sankey diagram	Showing flow volume between stages with branching and merging paths	—
Flowchart	Mapping process steps, decisions, and logic sequences	When order and conditions matter more than volume
Alluvial diagram	Showing how groups or categories reclassify over time	When tracking changes in composition across time periods
Funnel chart	Showing linear drop-off through a fixed sequence of stages	When flows only go in one direction with no branching
Chord diagram	Showing bidirectional relationships between peer categories	When flows are cyclic or between equal-level entities

When NOT to Use a Sankey Diagram

A Sankey diagram with the wrong data is harder to read than a plain table. Avoid them when:

• Your data has no directional flow. Comparing sales by region or revenue by product line is a bar chart problem, not a Sankey problem.
• You have too many nodes. More than 8–10 nodes per stage creates visual clutter that obscures the insight you are trying to show.
• Flows are very similar in size. When all bands have nearly the same width, the proportional advantage disappears, and a table communicates the data more clearly.
• You are tracking change over time only. A line chart handles temporal trends better; a Sankey is not a time-series tool.
• You have bidirectional or circular flows. Sankey diagrams are built for unidirectional, acyclic data. Loops distort the structure; use a chord diagram instead.

Best Practices for Sankey Diagrams

The difference between a Sankey that clarifies and one that confuses is usually in the setup, not the data.

• Limit stages to 4–5 levels. More than five levels make the diagram hard to follow; group minor flows into an “Other” node.
• Use distinct colors per source or category group — not per link. Consistent color per origin makes the paths traceable as they fan out.
• Label every significant node and the largest links. Tooltips help with detail, but key values should be visible without hovering.
• Sort nodes by flow size. Placing the largest flows at the top of each stage reduces link crossings and improves readability.
• Group small flows. Links that individually represent less than 2–3% of the total add noise; combine them into a single “Other” category.

How to Read a Sankey Diagram

Start on the left. Source nodes represent the origin of your flow traffic channels, budget sources, or input categories. Follow each band to the right:

• Thicker bands carry more volume. The width is always proportional to the value.
• Where a band splits, the flow is divided into multiple destinations.
• Where bands merge into a single node, multiple sources are combining.
• Hover tooltips (in interactive versions) show the exact volume on each link.

Bottlenecks appear where a wide incoming band feeds a much narrower outgoing one. Large drops between stages are immediately visible; you do not need to calculate them from a table.

Sankey Diagrams in ClicData

ClicData’s Visualization & Reporting module includes Sankey diagrams as a native chart type within its dashboard builder. You can build and configure one directly in the browser, no installation or coding required.

In ClicData, a Sankey diagram lets you:

• Visualize flow between source-target pairs from any connected dataset
• Customize node colors and alignment to match your brand or reporting standards
• Use hover effects to reveal exact volumes and flow percentages on each link
• Combine data from multiple sources, CRM, web analytics, and financial systems in a single dashboard

Because ClicData connects directly to your data warehouse, the diagram reflects live data each time the dashboard loads. There is no manual export or CSV upload involved.

ClicData’s dashboard editor also supports Power BI and Excel plugins. If you prefer to analyze Sankey-structured data in Power BI, you can connect your ClicData data warehouse directly via the Power BI connector.

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FAQ: Sankey Diagrams