Sankey Diagram vs Stacked Bar Chart: Which to Use
A stacked bar shows part-to-whole within each category; a Sankey shows how a quantity moves from one set of categories to another. See the same data both ways and choose.
A stacked bar answers what each category is made of. A Sankey answers where each category's amount goes. The data is the same, and the question decides which one is right.
The example has three departments spending a 900 k€ budget on people, tools and other costs. As a stacked bar you would see three columns, each divided into three colours. As a Sankey you see the departments flow into the cost types, and the totals of the cost types appear on the right.
The Sankey is stronger when you care about the cost types in total as well as by department, since both sides have a total. The stacked bar is stronger when you want to compare departments precisely.
What each does best
The two charts have different strengths.
- Stacked bar: precise comparison of totals across categories and of one part across categories.
- Stacked bar: easy to read, supported everywhere.
- Sankey: shows both sides of a many-to-many split at once.
- Sankey: shows chains with more than two levels.
Where each struggles
Stacked bars get hard to read when there are more than about five segments, and comparing the middle segments is imprecise. Sankey ribbons are harder to measure than bar lengths, so important numbers should be printed.
A rule of thumb
If there is one level of categories and the question is how big, use a bar. If there are two or more levels and the question is where it goes, use a Sankey.
Key points
- A 900 k€ budget: Engineering 400, Marketing 300, Operations 200.
- People are 58% of spend (520 k€), tools 26% (230 k€) and other costs 17% (150 k€).
- The right-hand side adds a total for each cost type that a stacked bar leaves implicit.
- The figures are invented.
The example’s data
Invented budget, balanced at every node.
| From | To | Amount (k€) |
|---|---|---|
| Marketing | People | 150 |
| Marketing | Tools | 90 |
| Marketing | Other | 60 |
| Engineering | People | 250 |
| Engineering | Tools | 100 |
| Engineering | Other | 50 |
| Operations | People | 120 |
| Operations | Tools | 40 |
| Operations | Other | 40 |
The same data as CSV
source,target,value
Marketing,People,150
Marketing,Tools,90
Marketing,Other,60
Engineering,People,250
Engineering,Tools,100
Engineering,Other,50
Operations,People,120
Operations,Tools,40
Operations,Other,40How it works
Write the question
Is it how big each category is, or where each amount goes?
Count the levels
One level of categories points to a bar; two or more point to a Sankey.
Draw both if unsure
The same table makes either, so try both and see which reads better.
Print the key numbers
Label the important figures on whichever chart you choose.
Frequently asked questions
Can I convert a stacked bar into a Sankey?
Yes. Each bar becomes a source node, each segment colour a target node and each segment a flow with its value.
Which is better for a presentation?
A bar for a simple point, a Sankey when the audience needs to follow the movement between two sets of categories.
Edit this budget Sankey
Open the example as your own chart and replace the budget with yours.
