Stacked Area Chart
Multiple area layers stacked on top of each other, showing how individual parts contribute to a total over time — part-to-whole meets time series.
// 01 — The chart
What it looks like
A stacked area chart showing quarterly revenue growth across three product lines. The top line represents total revenue.
// 02 — Definition
What is a stacked area chart?
A stacked area chart is an extension of the basic area chart where multiple data series are layered on top of each other. Each layer’s thickness represents that series’ value at any point in time, while the top edge of the entire stack shows the combined total.
This dual capability — showing both individual contributions and the aggregate — makes stacked area charts uniquely powerful for answering questions like “How did total revenue grow, and which segments drove that growth?”
There are two main variants: absolute stacked areas (where the Y-axis shows raw values) and 100% stacked areas (where the Y-axis shows percentages, normalizing all time points to 100%). The absolute version emphasizes changes in total magnitude; the percentage version emphasizes shifts in composition.
Key insight: In a stacked area chart, only the bottom layer’s values can be read accurately against the baseline. Upper layers require you to judge thickness, which is perceptually harder — one of the chart’s key trade-offs.
// 03 — Anatomy
Parts of a stacked area chart
// 04 — Usage
When to use it — and when not to
- Showing how a total changes over time while revealing each component's contribution
- You have 2–5 data series that sum to a meaningful whole
- The total trend and the individual breakdowns both matter
- Showing market share evolution, revenue mix, or traffic by source over time
- Your audience cares about both magnitude and composition
- You have more than 5–6 series — too many layers become unreadable
- Precise comparison between individual series is critical — use small multiples instead
- Series values are very similar, making it hard to distinguish layer thicknesses
- Data is not time-series or has no natural order on the x-axis
- Negative values are present — stacking breaks with negatives
// 05 — Reading guide
How to read a stacked area chart
Follow these steps whenever you encounter a stacked area chart.
Read the top line first
The upper boundary of the entire stack shows the total across all series. Follow this line to understand the overall trend — is the total growing, shrinking, or flat?
Identify each layer from the legend
Each coloured band represents a different category. Match the colours to the legend to understand what each layer represents.
Judge layer thickness, not position
The value of each series at any point is encoded by the thickness of its band, not its vertical position. A layer that appears high on the chart but thin contributes less than a thick band near the bottom.
Watch for layer order effects
The bottom layer is easiest to read precisely because it sits on a flat baseline. Upper layers are harder to judge because they float above uneven surfaces — keep this in mind.
Look for squeezing or expanding
If one layer grows while others shrink, that category is taking share. If all layers grow proportionally, the composition is stable even though the total is increasing.
// 06 — Data format
What data you need
A stacked area chart requires a time column plus one numeric column per series. Each row represents one time point, and the values in each series column are stacked vertically. All values must be non-negative.
// 07 — Construction
How to build one
Step 1: Choose a consistent time axis (x) and value axis (y). Ensure the y-axis starts at zero.
Step 2: Stack the series by drawing the bottom series as a normal area first, then adding each subsequent series on top of the previous one’s upper boundary.
Step 3: Assign distinct colours or opacities to each layer. Use a sequential palette if the series have a natural order, or a categorical palette otherwise.
Step 4: Add a legend and consider adding a tooltip that shows individual and total values at each time point.
// 08 — Common mistakes
Mistakes to avoid
Too many layers
More than 5–6 series makes the chart unreadable. Aggregate minor categories into an 'Other' group or use small multiples.
Poor colour choices
Layers with similar colours are impossible to distinguish. Use distinct hues or varying opacity levels with good contrast.
Y-axis not starting at zero
Truncating the y-axis distorts the perceived volume of each layer. The filled areas become visually misleading.
Confusing position with value
Upper layers may appear to 'dip' even though their values are stable — the visual shape is warped by the layers beneath.
Using stacked areas for unrelated series
Stacking only makes sense when the series sum to a meaningful total. Don't stack unrelated metrics like revenue and headcount.
// 09 — Real-world examples
Where you’ll see them
Google Analytics
Traffic by channel (organic, paid, social, direct) over time is one of the most common stacked area chart examples in the wild.
Energy reports
The IEA and EIA use stacked area charts extensively to show global energy consumption broken down by source — coal, oil, gas, nuclear, renewables.
COVID dashboards
Case counts by region were commonly shown as stacked areas, letting readers see both total case trends and regional breakdowns.
// 10 — Quick reference
Key facts
// 11 — Accessibility
Making it accessible
Use colours that are distinguishable by colourblind users. Pair colour with texture or patterns when possible. Add an aria-label summarising the overall trend and provide the underlying data in a table for screen reader users.
// 12 — Variations
Common variations
100% stacked area
Normalises each time point to 100%, showing only the proportional composition over time.
Streamgraph
Centres the baseline around the middle instead of starting from zero, creating a flowing, organic shape.
Stacked area with annotations
Key events or milestones are annotated on the chart to explain shifts in the stack.
Small-multiple areas
Instead of stacking, show each series in its own panel so readers can compare trends without visual interference.
// 13 — FAQs
Frequently asked questions
What is a stacked area chart?+
A stacked area chart is an extension of the basic area chart where multiple data series are layered on top of each other. Each layer's thickness represents that series' value at any point in time, while the top edge of the entire stack shows the combined total.
When should you use a stacked area chart?+
Use a stacked area chart when showing how a total changes over time while revealing each component's contribution. It also works well when you have 2–5 data series that sum to a meaningful whole, and when the total trend and the individual breakdowns both matter.
When should you avoid a stacked area chart?+
Avoid a stacked area chart when you have more than 5–6 series — too many layers become unreadable. It is also a poor fit when precise comparison between individual series is critical — use small multiples instead, or when series values are very similar, making it hard to distinguish layer thicknesses.
What data do you need to make a stacked area chart?+
A stacked area chart requires a time column plus one numeric column per series. Each row represents one time point, and the values in each series column are stacked vertically. All values must be non-negative.
How is a stacked area chart different from an area chart?+
Both a stacked area chart and an area chart can look similar at first glance, but they answer different questions. Reach for a stacked area chart when the comparisons and patterns it was designed to reveal match what you need to communicate, and choose an area chart when its particular strengths better fit your data and audience.
What is another name for a stacked area chart?+
Stacked Area Chart is also known as Layered area chart, cumulative area chart. The name varies between fields, but the visualisation technique is the same.
What size of dataset works best for a stacked area chart?+
Stacked Area Chart works best for 2–5 series with a meaningful total. Outside that range the chart either looks empty or becomes too cluttered to read clearly.
Are stacked area charts accessible to screen readers?+
Use colours that are distinguishable by colourblind users. Pair colour with texture or patterns when possible. Add an aria-label summarising the overall trend and provide the underlying data in a table for screen reader users.