What Is a Sankey Diagram? A Beginner-Friendly Explainer

If you have ever seen a chart where colored bands flow from one column of labels to another—growing wider or narrower along the way—you were looking at a Sankey diagram. Named after Irish engineer Captain Matthew Sankey, who used one in 1898 to illustrate steam-engine energy efficiency, Sankey diagrams remain one of the most powerful ways to visualize flows, transfers, and processes.

In this guide we cover what a Sankey diagram is, how to read one, real-world use cases, and how to build your own with ChartLoad’s free Sankey maker.

How to Read a Sankey Diagram

A Sankey diagram consists of three elements:

• Nodes – Rectangles or labels representing entities (e.g., departments, energy sources, funnel stages).
• Links (flows) – Curved bands connecting nodes. The width of each band is proportional to the quantity it represents.
• Direction – Flows move left-to-right (or top-to-bottom), showing how a total is distributed or transformed.

The key insight is that the total width entering a node equals the total width leaving it (conservation of flow). This makes it easy to see where the biggest transfers happen and where losses occur.

Real-World Sankey Diagram Examples

1. Energy Flow

The U.S. Energy Information Administration publishes annual Sankey diagrams showing how energy from sources (solar, natural gas, nuclear) flows through sectors (residential, industrial, transport) and ends as either useful energy or rejected waste. A single diagram replaces pages of tables.

2. Budget Allocation

Companies use Sankey diagrams to show how total revenue splits into cost of goods sold, operating expenses, taxes, and net profit. The visual width makes it immediately clear which cost center consumes the most.

3. User Journey / Website Traffic

Marketing teams map how visitors flow from landing pages through product pages to checkout—or drop off. This is similar to a funnel chart, but Sankeys handle multiple branching paths that funnels cannot.

4. Supply Chain

Trace raw materials from suppliers through manufacturing stages to distribution centers and retail outlets. Width reveals bottleneck routes at a glance.

Sankey Diagram vs Funnel Chart

If your process is a simple linear pipeline, a funnel chart is quicker to build and easier to read. When paths branch or merge, the Sankey is indispensable.

When to Use a Sankey Diagram

• Showing energy or material balance with conservation of quantity.
• Visualizing multi-step user flows with branching (e.g., A/B test paths).
• Illustrating budget or cost breakdowns with more than one level of hierarchy.
• Mapping migration patterns—population moving between regions or job roles.

When a Sankey Is NOT the Best Choice

• Comparing categories side by side – Use a bar chart.
• Showing proportions of a single whole – A pie chart, donut chart, or treemap is simpler.
• Time-series data – A line chart or area chart communicates trends more clearly.
• Too many nodes – Beyond 20–25 nodes the diagram becomes spaghetti. Aggregate small flows into an “Other” category.

How to Create a Sankey Diagram in ChartLoad

1. Open the ChartLoad Sankey Diagram Maker.
2. Enter your data as source → target → value rows. Example: Solar → Electricity → 45.
3. ChartLoad automatically positions nodes and calculates flow widths.
4. Customize colors per node or per flow for storytelling emphasis.
5. Export as PNG, SVG, or grab the embed code.

“Sankey diagrams are the X-ray of processes—they reveal where the real volume goes.”

Design Tips

• Use distinct colors for each source node so flows are traceable across the diagram.
• Label both nodes and large flows with values for precision.
• Keep the number of stages (columns) to 3–5 for readability.
• Pair with a summary waterfall chart if stakeholders also need a cumulative running total.

For a broader view of which visualization fits your data, read how to choose the right chart or explore our full data visualization examples gallery.

Ready to map your own flows? Create a free Sankey diagram at ChartLoad.com—no account, no watermarks, no limits.