A Sankey diagram is a type of flow diagram that helps visualize the flow of quantities, such as energy, materials, or costs, between different stages or components of a system. The width of each arrow in the diagram is proportional to the amount of the quantity it represents.

Sankey diagrams feature directed arrows that have a width proportional to the flow quantity visualized: if a flow is twice as wide it represents double the quantity. Flow diagrams can show e.g. energy, materials, water or costs. Within a Sankey chart the directed flow is always drawn between at least two nodes (processes).

A Sankey Diagram is a visualisation technique that allows to display flows. Several entities (nodes) are represented by rectangles or text. Their links are represented with arrow or arcs that have a width proportional to the importance of the flow.

How do Sankey diagrams work? Sankey diagrams are flow diagrams where the width of the flow is proportional to the volume of the flow. For example, if energy flow is visualized, a line representing 10 MW of energy would have double the thickness of a line representing 5 MW of energy.

As such, the Sankey diagram is a specific type of flowchart. This diagram is used to analyze, plan and demonstrate processes in a simple way. Each of the steps in the process is represented by different geometric figures that signify a specific type of step. It is also symbolized by arrows that indicate the order and flow of the categories.