Sankey Diagram
A type of flow chart that visually represents how quantities move or transform from one stage to another. The defining feature of is its proportional flow lines, where the width of each arrow corresponds to the size or magnitude or precentage of the flow it represents. This makes it easy to see where resources such as energy, money, materials, or time are distributed, combined, or lost across a process or system. The result is a powerful storytelling tool that combines data analysis with visual impact, helping stakeholders grasp relationships that might be overlooked in tables or text alone.
Originally used in engineering and energy management, Sankey diagrams have become popular in business, sustainability, and analytics because they make complex data more understandable. The visual clarity helps teams quickly identify inefficiencies or imbalances in a process.
Examples include:
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- revenue flows through different departments
- solid or hazardous waste generated in a manufacturing process
- energy or water usage or carbon emissions broken down into process areas or departments
- production shift time by process losses (OEE)
- website traffic clicks
- political election outcomes (2025 New York City mayoral race)
Creating a Sankey diagram typically involves mapping inputs, outputs, and transitions between stages, then assigning quantitative values to each connection.
Tools like Power BI, Flourish, Google Charts, and specialized software such as SankeyMATIC can automatically generate these visuals from data.
What types of data work best in a Sankey diagram?
They are ideal for quantitative flow data (numeric data that can be calculated into a percentage) for any dataset that shows how something moves, transfers, or transforms between categories.
How is a Sankey diagram different from a regular flowchart?
Unlike a standard flowchart, which focuses on sequence or process steps, a Sankey diagram emphasizes proportional relationships. The varying line thickness visually encodes the amount being transferred, allowing viewers to immediately see which flows dominate.
Can Sankey diagrams show inefficiency or waste?
Yes. One of their most valuable uses is to highlight losses or leakages. For example, energy lost as heat, scrap material in production, or budget overruns. By visualizing where resources diminish, organizations can target improvement opportunities more effectively.
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