The Sankey diagram is a specific type of flow chart, in which the width of the arrows is shown proportional to the amount of flow.

Sankey diagrams are named after Irish captain Matthew Henry Phineas Riall Sankey), who used this type of diagram in 1898 in a publication on the energy efficiency of the steam engine. Early black and white charts were used simply to show one type of flow (e.g., steam "Steam (state)").

One of the most famous Sankey diagrams is the map of Napoleon's campaign in Russia of 1812. It is a flowchart, overlaying a Sankey diagram on a geographic map. It was created in 1869 by Charles Minard").

Sankey diagrams are often used to visualize the transfers of energy, material or cost between processes, through arrows that show the loss or dispersion due to transfer. They are also used to display energy or material flow accounts at a regional or national level. These types of diagrams place visual emphasis on the important transfers or flows within a system, and are helpful in locating the dominant contributions to an overall flow. Sankey diagrams often show conserved quantities within the boundaries of a defined system, typically energy or mass, but can also be used to show flows of non-conserved quantities such as exergy; the latter are called Grassmann diagrams").

An example of an interactive application for producing Sankey diagrams is the Sankey web tool from Eurostat, the Statistical Office of the European Union. This tool allows the user to visualize energy balances through flowcharts and modify different options such as country, year, fuel, level of details, etc.

• - Thermodynamics.

• - Wikimedia Commons hosts a multimedia category on Sankey Diagram.

• - Scottish Executive - Energy in Scotland: Supply and Demand.

• - Examples of diagrams from Sankey Blog with all the information to get started in the world of flowcharts.

• - Irish Environmental Protection Agency Archived March 10, 2016 at the Wayback Machine. - Material Flow Accounts (MFAs) – Demonstration for Ireland - 2001].

• - sankey-diagrams.com – Blog discussing the usage of Sankey diagrams.