How to Make a Stacked Bar Chart in Looker

A stacked bar chart is one of the best ways to show how different segments contribute to a total, letting you see both the big picture and the details simultaneously. If you want to compare website traffic sources month-over-month or see how product categories stack up in your total revenue, this is the chart for you. In this tutorial, we will walk through exactly how to create, style, and interpret a stacked bar chart in Looker Studio (formerly Google Data Studio).

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When Should You Use a Stacked Bar Chart?

Before jumping into the builder, it helps to know when a stacked bar chart is the right tool for the job. These charts excel at comparing parts of a whole across different categories or points in time. Each bar represents a total, and the segments, or "stacks," within the bar show the relative contribution of each sub-component.

Here are a few common scenarios where a stacked bar chart shines:

• Marketing Campaign Performance: Visualizing total conversions per campaign, with stacks representing the contribution of different channels like Facebook Ads, Google Ads, and Email Marketing.
• Website Demographics: Showing total monthly visitors broken down by age group or device type (Mobile, Desktop, Tablet).
• Sales Revenue Analysis: Displaying total sales per quarter, with stacks broken down by product line or sales region.
• Project Management: Tracking hours worked on a project by team members each week, where each bar is a week and each stack is a team member.

Keep in mind, they work best when you have a limited number of segments to show. If you try to stack more than five or six categories, you can end up with a "rainbow" effect that's difficult to read and interpret. For those situations, a different chart type might be more appropriate.

Prepping Your Data for Looker Studio

Looker Studio can visualize nearly any data you throw at it, but it works best when your data is structured cleanly. A little bit of prep work ensures the charting process is smooth and error-free. The goal is to organize your data so that each row represents a single observation and each column represents a specific attribute.

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The 'Tidy Data' Structure

For a perfect stacked bar chart, your data source (like Google Sheets or a SQL table) ideally needs three types of columns:

• A Main Dimension: This will be the label for each bar on the axis. Think of it as the primary category you're measuring against. Examples include Date, Campaign Name, or Country.
• A Breakdown Dimension: This column contains the categories that will form the "stacks" within each bar. Examples are Traffic Source, Product Category, or Device Type.
• A Metric: This is the numerical value that determines the size of the stacks and the total height of the bar. Examples include Sessions, Revenue, or Conversions.

Here’s a simple Google Sheets example of properly structured data for charting website sessions by source over two months:

When you connect this beautifully organized data to Looker Studio, building a stacked bar chart becomes incredibly simple because you've already defined what each bar, stack, and value should be.

Step-by-Step: Building a Stacked Bar Chart in Looker Studio

Now for the fun part. Let's create a stacked bar chart from scratch. For this example, we’ll visualize monthly marketing leads broken down by their acquisition source, like Organic Search, Paid Social, and Referrals.

1. Adding the Chart to Your Canvas

First, open your Looker Studio report or create a new one. In the toolbar, click Add a chart and scroll down to the "Bar" section. You'll see several options, select the Stacked Bar Chart or the Stacked Column Chart (the choice just depends on whether you prefer horizontal or vertical bars). Drag the chart onto your report canvas and resize it as needed.

When you drop it onto the canvas, Looker will try to auto-populate it with data from the data source already connected to your report. Don't worry if it looks wrong at first, we're about to configure it properly.

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2. Configuring Dimensions and Metrics

With your new chart selected, a Properties Panel will appear on the right side of the screen. This panel has two main tabs: Set Up and Style. We'll start in the Set Up tab.

This is where you tell Looker how to draw the chart using the tidy data we discussed earlier:

• Data Source: Make sure the correct data source (e.g., your Google Sheet or Google Analytics account) is selected.
• Dimension: This is the primary category that defines each individual bar. For our example, we'd drag our 'Month' field here. Each bar will now represent a month.
• Breakdown Dimension: This is what creates the stacks within each bar. We’ll drag our 'Source' field here. Looker will now segment each monthly bar by Organic, Paid Social, etc.
• Metric: This is the numerical value. Drag your 'Leads' or 'Sessions' metric here. This determines the size of each colored segment.

As you drag these fields into place, you'll see your chart update in real-time. Just by setting these three fields, you should already have a functional stacked bar chart. Now, let’s make it look presentable.

Making Your Chart Readable: Styling and Formatting

A good chart doesn't just display data, it tells a story clearly and effectively. Moving to the Style tab in the Properties Panel allows you to fine-tune the appearance of your chart to improve readability.

Key Styling Options to Adjust

• Color by: By default, Looker adds colors. You can change them by setting "Color by" to "Breakdown dimension value" and manually assigning brand-aligned colors to each source (e.g., blue for Organic, green for Paid Social).
• Data Labels: Check the "Show data labels" box. This is one of the most important styling features for a stacked chart, as it displays the exact value of each segment directly on the chart, so your audience doesn't have to guess.
• Sorting: In the Set Up tab, you'll find sorting options. You can sort the main dimension (e.g., sorting months chronologically) and also sort the breakdown dimension to control the order of the stacks within each bar.
• Axes and Grid: Customize the axis labels, text size, and color. You can also clean up the chart by changing the grid color to something faint or by removing it entirely if you have data labels enabled.
• Legend: The legend explains what each colored stack represents. You can change its position (top, bottom, right) and text style. Place it where it’s most intuitive without cluttering the visualization.

By spending a few minutes in the Style tab, you can transform a generic, auto-generated chart into a clear, professional visualization that's easy for anyone to understand.

Going a Step Further: 100% Stacked Bar Charts

Sometimes, you're less interested in the raw totals and more interested in the proportion of each segment. For instance, what percentage of your total traffic came from mobile devices each month? A 100% stacked bar chart is built for this.

Instead of showing absolute values, it normalizes each bar to 100% and visualizes the relative contribution of each segment. This is fantastic for identifying trends in composition over time, like noticing that mobile traffic's share grew from 40% to 60% over the last year, even if total traffic went up and down.

Creating one in Looker Studio is simple. With your chart selected, go to the Style tab and find the checkbox labeled Show as 100% stacked. Check it, and Looker automatically converts your absolute values into percentages.

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Common Pitfalls and How to Avoid Them

While powerful, stacked bar charts can be misleading if not done correctly. Here are a few things to watch out for:

1. Overcrowding with too many stacks. As mentioned earlier, limit your breakdown dimension to a handful of segments. If you have more than five, consider grouping smaller segments into an "Other" category or choosing a different chart type.
2. Difficulty in comparison of middle stacks. The bottom stack in every bar shares a common baseline (zero), making it easy to compare. However, segments in the middle and top do not share a common baseline, making it hard to compare their lengths visually. If precise comparison between all segments is needed, a regular multi-bar chart might be better.
3. Not starting the axis at zero. Looker Studio does this automatically, but it bears repeating as a core principle of data visualization. Starting a bar chart axis at a value other than zero can dramatically distort the perception of the data and mislead your audience. Always ensure your baseline is set to zero.

Final Thoughts

Creating a stacked bar chart in Looker Studio is a fantastic way to represent how different components contribute to a whole across various categories. With your data structured neatly, you can build an insightful and professional-looking chart in just a few clicks, making your reports more dynamic and valuable for your team or clients.

While it is rewarding to build reports manually in Looker Studio, we know that constantly pulling data from different places and keeping multiple dashboards updated takes valuable time away from actual analysis. At Graphed, we created a way to skip the manual setup entirely. I connect all my marketing and sales data sources just once, then I can create real-time reports and dashboards simply by describing what I need in plain English - like asking, "Show me a stacked bar chart of traffic by source for the last quarter." It turns hours of report building into a 30-second conversation, freeing you up to focus on the insights, not just the clicks.