What Are Sankey Graphs? And Why They're So Useful

Have you ever tried to explain where all your energy, money, or time goes—and found yourself tangled in numbers and arrows on a regular chart? If yes, a Sankey graph might be exactly what you need.

Sankey graphs (also known as Sankey diagrams) are special types of flow charts designed to show how something moves or gets distributed between different parts of a system. Whether you're analyzing where your marketing budget went or understanding energy use in a factory, Sankey diagrams help make complex processes visual and much easier to grasp.

In this blog, we’ll explain what Sankey graphs are, why they’re so helpful, when you should (and shouldn’t) use them, and where they’re being used today.

What is a Sankey Graph?

A Sankey graph is a type of flow diagram where the width of the lines (also called "flows" or "links") represents the quantity of whatever is moving through the system—be it energy, money, materials, or people.

Think of it like a river map: wider rivers carry more water. In a Sankey diagram, thicker lines mean a greater volume or value.

These diagrams connect "nodes" (which represent categories, steps, or systems) with "links" (the flows between them). It’s a way of visually mapping out how resources enter, move through, and exit a process.

Why Sankey Graphs Are So Useful

1. They show where stuff goes—clearly

Unlike bar or pie charts that only show how big something is, Sankey diagrams show how things move. For example, if you want to track how energy flows from generation to usage or how money flows through a business, a Sankey diagram makes it easy to see.

2. They highlight the biggest players

Since line thickness shows quantity, it’s easy to spot which areas have the biggest impact. You can instantly identify the largest source of waste, cost, or inefficiency.

3. They simplify complexity

Sankey diagrams can condense a complicated system into a clear visual. A system that might take several spreadsheets to explain can often be shown in one powerful image.

4. Great for storytelling

They’re not just about data—they tell a story. You can guide your viewer’s eye from beginning to end, helping them understand a process step by step.

When Should You Use a Sankey Graph?

Sankey diagrams shine in situations where flow and relationships are key. Here are some good use cases:

• Energy usage: See where energy is lost in a system.
• Budget tracking: Follow how money flows across departments or campaigns.
• Supply chains: Visualize how materials move from suppliers to consumers.
• Website analytics: Track user navigation paths on a website.
• Manufacturing: Understand the flow of materials, time, or cost in production.

When NOT to Use a Sankey Diagram

As powerful as they are, Sankey graphs aren’t always the best tool. Here’s when to think twice:

• Your audience is new to data visualization: These graphs can be confusing without explanation.
• Flows are nearly equal: If the differences in flow size are small, they can be hard to notice.
• There’s not enough space: In a crowded layout, links can overlap and clutter the diagram.

You don’t have clear quantities: Since line width is based on value, vague or non-numeric data won’t work well.

Tips Before Creating a Sankey Diagram

Before jumping into making one, ask yourself:

• What am I trying to show? Is it a story, a problem area, or just an overview?
• Who is my audience? Are they comfortable reading advanced charts?
• What’s the key takeaway? Is it a bottleneck, a large loss, or an efficiency?

These questions help you make a Sankey graph that’s not just pretty—but actually useful.

Real-Life Examples & Use Cases

Sankey diagrams aren’t just for scientists or engineers. They’re used in many industries:

Energy & Environment

Used to analyze energy flows, like how much energy is generated vs. lost in transmission or how renewable energy is distributed.

Business & Finance

Track where your marketing budget went and what brought in the most returns. It’s great for ROI analysis.

Manufacturing

Visualize how raw materials become final products and where resources are wasted in the process.

Supply Chain Management

See how goods move across stages, from production to distribution. It can help identify delays or high-cost areas.

Web Analytics

In digital marketing, tools like Google Analytics use Sankey-style visuals (also called “user flow”) to show how visitors move through a website.

Horizontal vs. Vertical Sankey Diagrams

Sankey diagrams can be laid out in two main ways:

Horizontal Sankey: Flow goes left to right. Commonly used in energy flow and business data.

Vertical Sankey: Flow moves top to bottom. These are used when vertical layout fits better in dashboards or mobile views.

The layout doesn’t change the data—just the way it's displayed for readability.

Tools You Can Use to Create Sankey Diagrams

Want to make one yourself? Here are some popular tools:

FusionCharts: Offers interactive Sankey diagrams with easy integrations.

Google Charts: Free and good for simple Sankey diagrams.

Tableau or Power BI: Can create Sankey-style visuals with some effort.

Final Thoughts: Make Data Flow Make Sense

Sankey diagrams are more than just pretty visuals—they’re a powerful way to understand, explain, and improve complex processes. Whether you're a business analyst, energy consultant, marketer, or student, learning how to use Sankey graphs can take your data storytelling to the next level.

Just remember to use them wisely. When used right, they can turn confusing data into clear insights. When used poorly, they can overwhelm or mislead.

So next time someone asks, “Where does it all go?” — you’ll have just the chart to show them.