How to Make a Double Bar Graph in Looker
Comparing performance is at the heart of insightful data analysis, and a double bar graph is one of the clearest ways to visualize that comparison. Whether you're tracking this month's revenue against last month's or comparing traffic from different marketing channels, seeing the data side by side tells a powerful story. This article will guide you through the exact steps to create a versatile double bar graph, often called a grouped bar chart, in Google's Looker Studio.
Why Use a Double Bar Graph?
A double bar graph excels at showing a direct comparison between two sets of data across several categories. Unlike a stacked bar chart, which shows parts of a whole, a grouped bar chart places bars next to each other, making it easy to see which category performed better for each metric. It removes the guesswork and makes relative performance instantly obvious.
Here are some common scenarios where this chart type is incredibly useful:
Time-Based Comparisons: Seeing week-over-week, month-over-month (MoM), or year-over-year (YoY) performance for key metrics like sales, traffic, or leads.
Segment Comparisons: Comparing user behavior across segments like Mobile vs. Desktop, or New vs. Returning Visitors.
Campaign Performance: Visualizing metrics like clicks and impressions for a set of campaigns to see their relative efficiency.
Product Sales: Comparing the sales figures of different products against each other over the same period.
Understanding the Data You Need
Before you jump into Looker Studio, it helps to understand what data structure you need. To build a double bar graph, you'll need three key ingredients:
One Dimension: This is the categorical data you want to display on the x-axis. It’s what you are grouping your comparison by. Examples include Campaign Name, Traffic Source, Country, or Date.
Two Metrics: These are the numerical values being measured for each category in your dimension. Looker Studio will draw a separate bar for each metric. For example, your metrics could be Sessions (This Period) and Sessions (Previous Period), or Mobile Sales and Desktop Sales.
Getting your data structured this way is the most important step. Don't worry - Looker Studio has powerful built-in features that make this seamless, especially for date comparisons.
Step-by-Step: Creating a MoM Comparison Chart
The most common use for a double bar graph is period-over-period comparison. Let’s build a chart that compares website sessions by traffic source for the last 30 days against the 30 days prior.
Step 1: Add a Chart and Connect Your Data
Start inside your Looker Studio report. If you don't already have a data source connected, add one - we’ll use Google Analytics for this example.
Navigate to the toolbar and click Add a chart.
From the dropdown, select one of the Bar chart options. A simple Bar chart will work perfectly.
Place the new chart onto your report canvas. Looker will populate it with default data.
Step 2: Set Up Your Dimension
With your new bar chart selected, a Setup panel will appear on the right side of your screen. This is where you'll tell Looker Studio what data to show.
In the "Dimension" section, drag and drop the field you want to analyze. For our example, we want to see traffic by source, so we will use the Session default channel group dimension from Google Analytics.
Step 3: Define Your Date Range and Comparison
This next step is where the magic happens. Here, we'll configure Looker Studio to automatically create our two metrics: sessions from this period and sessions from the last period.
In the Setup panel, scroll down to the Default date range section.
Click on it and select a predefined period like Last 30 days or set a custom range. This defines your primary period.
Just below, click on Comparison date range. A menu will appear. Select Previous period. This tells Looker to pull data from the 30 days directly preceding your main date range.
When you apply this, Looker Studio instantly works its magic. It automatically generates a second set of data for the comparison period and plots it right next to your original data, creating a double bar graph. Your chart will now show sessions from the last 30 days side by side with sessions from the 30 days before that, for each traffic source.
Step 4: Clean Up and Style Your Chart
Your chart is functional, but a few style adjustments will make it much easier to read and understand.
With the chart selected, click the Style tab in the right-hand panel.
Colors: You can assign distinct colors to each bar. For instance, make your current period a dark blue and the previous period a lighter shade of blue. This creates a clear visual relationship between the two metrics.
Labels: Check the box for Show data labels. This will display the actual numerical value on top of each bar, saving your audience from having to guess or interpret the axis.
Legend: Adjust the legend font and position (e.g., top, bottom, right) to make it clear which color corresponds to which period. We recommend renaming your metrics in the 'Setup' tab for ultimate clarity. For instance, you could rename "Sessions ∆" to "Sessions (Previous Period)".
Gridlines: Sometimes, less is more. You might consider changing the grid color to a very light grey or removing it entirely to make the bars stand out more.
Following these steps gives you a clean, clear, and professional-looking double bar graph that effectively communicates performance trends.
Alternative Method: Using Blended Data
What if your two metrics come from different data sources? For example, you want to compare Ad Spend (from Google Ads) with Revenue (from Shopify) for the same campaigns. Looker's "Comparison date range" feature won’t work here. Instead, you'll need to use blended data.
Data blending allows you to "join" two or more data sources together based on a common key, also known as a join condition.
From the top menu, navigate to Resource > Manage blended data.
Click Add a data blend. This opens the data blending interface.
Add your first data source (e.g., Google Ads). Select a common dimension to join on, like Campaign, and the metric you want, like Cost.
Click Join another table and add your second data source (e.g., Shopify). Select the same join dimension (you may need to ensure it's named identically or use fields with the same values) and add your second metric, like Total sales.
Looker Studio will ask you to configure the "join." An inner join is good if you only want to see campaigns present in both data sets.
Save the new blended data source.
Now, you can create a bar chart using this new blended source. Set your dimension to Campaign and then you can add both Cost and Total sales as your two metrics, creating a side-by-side comparison without any date tricks.
Common Mistakes to Avoid
Creating double bar graphs is straightforward, but a few common slip-ups can make them confusing.
Forgetting to Set the Comparison Range: The number one issue is simply forgetting to add a comparison date range. Without it, you’ll only have a single bar chart.
Accidentally Using a Stacked Bar Chart: With the chart selected, look at the Style panel. Make sure that the "Stacked Bars" option is turned off. Stacking the bars adds their values together, which isn't what you want for a direct comparison.
Using Mismatched Scales: If one metric is in the thousands (like sessions) and another is in the tens (like conversion rate), plotting them on the same axis will make one nearly invisible. In this case, consider a "Combination chart" where you can use a second axis for the second metric.
Poor Labeling: Always give your chart a clear title (e.g., "MoM Organic vs. Paid Traffic"). If your metric names are auto-generated, rename them to be reader-friendly. Avoid acronyms and technical names that stakeholders might not understand.
Final Thoughts
Now you have a complete game plan for creating effective double bar graphs in Looker Studio. Whether you use the simple date comparison feature for time-series analysis or blend data for more complex scenarios, this chart type is essential for any reporting dashboard that aims to show what's moving in your business.
While Looker Studio is powerful, manually setting up charts, remembering to configure date ranges correctly, and blending your data sources still take time and focus away from a more important task: acting on the insights. That’s why we built Graphed. We connect all your critical marketing and sales tools - from Google Analytics to Shopify and Salesforce - so you can skip the setup entirely. To get the chart we just built, you would simply ask, "create a bar chart comparing website sessions by source for the last 30 days vs the previous 30 days," and our AI data analyst would instantly build it for you with real-time data.