How much flows through your process? Add the volumes with a Sankey
A process map answers who does what, in what order. It does not answer how many: how many orders take the happy path, how many are back-ordered, how many are cancelled. Draw the same process as a Sankey diagram and the volumes become the picture, so the path that carries most of the work, and the one that leaks it, is obvious at a glance.
Two diagrams, two questions
A swimlane process map is the right tool for agreeing how a process works: every step, the role responsible for it, the decisions and the handoffs between teams. Every path is drawn the same width, because the map is about the rules, not the traffic.
A Sankey diagram is the right tool for showing how a process performs: each band is as wide as the number of cases that take that path. The two belong together. The map tells a new colleague what to do; the Sankey tells a manager where the time and money go.
From map to Sankey, step by step
Start from the process map you already have. You do not need every box: keep the steps where the work splits, merges or leaves the process, and drop the ones every case passes through in a straight line.
- Each kept step becomes a node: "Orders received", "Picked in full", "Back-ordered"
- Each arrow between kept steps becomes a flow
- Each outcome (delivered, cancelled, returned) becomes an end node, so nothing disappears off the edge
- Put one month's count on every flow, in one unit: orders, tickets, applications
A worked example: one month of orders
Take 1,000 orders received in a month. 900 are picked in full, 70 are back-ordered, and 30 are cancelled before picking. Of the 70 back-ordered, 55 ship late and 15 are cancelled. In SankeyCharts.app that is six rows: Orders received flows to Picked in full (900), Back-ordered (70) and Cancelled (30); Back-ordered flows to Shipped late (55) and Cancelled (15).
The diagram makes two things obvious that the map could not. The back-order path is small (7% of orders) but it produces a third of all cancellations. And because Cancelled is one node fed from two places, its total (45) is drawn once, as one bar, instead of being split across the map.
Rework and loops
Real processes send work backwards: an order sent back for a correct address, a document returned for a signature. On a process map that is an arrow pointing upstream. On a Sankey it is a flow back to an earlier node, and SankeyCharts.app draws it as a return line under the diagram, so the volume of rework is visible without tangling the forward flows.
Keep the numbers honest
Every intermediate step should balance: what arrives at it in a month should leave it. When it doesn't, the editor shows the difference on the node. Usually that means a missing path, such as cases still in progress at month end, and the fix is to add it as its own end node ("Still open") rather than to round the numbers until they match.
Frequently asked questions
Can a process map show volumes?
Not well. A process map draws every path the same width, because its job is the rules. A Sankey diagram of the same process draws each path as wide as its volume, so the two are best used side by side.
Which steps of a process map should go into the Sankey?
The steps where work splits, merges or leaves the process, plus an end node for every outcome. Steps every case passes through in a straight line add columns without adding information.
Try it on your own numbers
The editor is free and opens with a starter Sankey diagram. One row per node, and the diagram draws itself as you type. No signup required.
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