Charts & Visualizations

Sankey Diagram

A flow diagram where the width of arrows represents the quantity of flow.

Definition

Sankey diagrams visualize flows (e.g., energy, materials, money, web traffic) between nodes or stages in a process. The width of the connecting bands (links) is directly proportional to the flow quantity, making it easy to see major contributions, pathways, and losses within a system.

Examples

Material flow through a production process with waste and rework

Chart Visualization

This example includes an interactive chart visualization with 6 data points.

Chart type: sankey

Usage

Best Used For

  • Visualizing flow quantities between stages or categories
  • Showing energy balances, material flows, or cost breakdowns
  • Analyzing resource allocation, website navigation paths, or process efficiency
  • Tracking conversions, diversions, or losses through a system

Data Requirements

[Object]

When to use this chart

Multi-touch paths

Data shape: Channel → landing → product → purchase flow volume

Link width = volume; ideal for branching journeys a linear funnel cannot represent

Source: Schmidt (2008), Sankey original; Google Analytics pathing reports

Limitations

Important Considerations

  • ⚠Can become complex and hard to follow with many nodes and crossing flows
  • ⚠Layout can be sensitive to node ordering and link arrangement
  • ⚠Not ideal for visualizing cyclical flows (loops)
  • ⚠Reading exact flow values can be difficult; relies on proportional width

Best Used For

  • Visualizing flow quantities between stages or categories
  • Showing energy balances, material flows, or cost breakdowns
  • Analyzing resource allocation, website navigation paths, or process efficiency
  • Tracking conversions, diversions, or losses through a system

Supplemental Resources

Frequently asked questions

Common questions about Sankey Diagram, answered.

What is a Sankey diagram?
A Sankey diagram visualizes flow through a system as a set of nodes (stages) connected by links whose width is proportional to the quantity flowing along them. It traces how a total splits, merges, and moves from sources on one side to destinations on the other — energy through a process, users through pages, budget across allocations. The varying link widths make it instantly clear where the big flows and the leaks are.
When should I use a Sankey diagram?
Use one to show directional, multi-stage flow where you want to see how quantities move and divide between steps — user journeys across pages, conversion paths, budget allocation, or attribution flow from channels to outcomes. Its strength is revealing the dominant paths and where volume drops out. Avoid it for simple two-stage comparisons (a bar chart is clearer) or when flows aren't directional (a chord diagram suits relationships better).
How do I read a Sankey diagram?
Follow the flow left to right (or top to bottom). Nodes are stages; the links between them are flows, and a wider link means more volume. Where a node's incoming width is larger than its outgoing width, volume was lost at that stage; where links fan out, the flow split between destinations. Trace a single thick path to see the dominant route, and look for nodes where large inflows shrink to small outflows — those are your leaks.
Sankey diagram vs funnel chart — which should I use?
A funnel chart shows a single linear sequence with simple stage-to-stage drop-off. A Sankey handles branching and merging — when items split across multiple paths or recombine — which a funnel can't represent. Use a funnel for one straight conversion sequence; use a Sankey when the journey branches, when there are multiple sources or destinations, or when you need to see how flows redistribute between stages.
What are the limitations of a Sankey diagram?
They get cluttered with too many nodes or crossing links, and reading exact values from link widths is approximate, so they're better for proportions than precise figures. They also assume conservation of flow (what enters a node should be accounted for leaving it), so messy or non-conserving data can confuse. Keep the number of nodes manageable, order them to minimize crossings, and add labels or tooltips for exact numbers.

Related Terms

Network Graph

Related term

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Chord Diagram

Related term

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Data Visualization