How to Make a Comparison Chart in Looker

Comparing performance metrics is at the heart of any effective data analysis. You're not just looking at this month’s numbers, you’re looking at them in relation to last month’s, last year’s, or against another campaign. This article will show you how to create powerful comparison charts in Looker Studio (formerly Google Data Studio) to visualize performance, track progress, and uncover meaningful insights.

Why Bother with a Comparison Chart, Anyway?

A single number, like "10,000 website sessions," doesn’t tell you much on its own. Is that good? Bad? About average? A comparison chart provides the context needed to answer those questions. By placing data points side-by-side, you immediately begin to understand performance in a more meaningful way.

Here are a few common scenarios where comparison charts are indispensable:

• Time-Based Comparisons: The most frequent use case. This includes looking at performance Month-over-Month (MoM), Quarter-over-Quarter (QoQ), or Year-over-Year (YoY). Are your Q3 sales better than last year's Q3? Did your blog traffic grow from March to April?

• Campaign Performance: Directly compare the results of two different marketing campaigns. See which Facebook ad set drove more conversions or which email promotion had a higher click-through rate.

• Channel Analysis: Evaluate how different acquisition channels stack up against each other. A bar chart comparing traffic from Organic Search, Paid Social, and Direct traffic can quickly show you where your audience is coming from.

• A/B Test Results: Visualize the results of a landing page test by comparing conversion rates for Version A against Version B.

• Product or Regional Sales: An e-commerce business might compare the sales performance of different product categories or see which geographic regions are driving the most revenue.

In short, comparisons turn raw data into a story about what’s working, what’s not, and where trends are heading.

Before You Build: Prepping Your Data in Looker Studio

Before you start adding charts, a little preparation goes a long way. Getting your data foundation right ensures your charts will be accurate and easy to build.

Step 1: Connect Your Data Source

Looker Studio thrives on data connectors. To begin, you need to add a data source to your report. If you haven't already, go to Resource > Manage added data sources and click “ADD A DATA SOURCE.”

For most time-based comparisons, Google Analytics is a popular choice. For comparing campaign performance across different platforms, you might use Google Sheets where you’ve aggregated data from Facebook Ads, LinkedIn Ads, and other sources.

Step 2: Understand Your Metrics and Dimensions

Once your data is connected, it’s vital to know the difference between Dimensions and Metrics. Think of it this way:

• Dimensions: These are the categories you use to segment your data. They are often text-based. Examples include Date, Campaign Name, Channel, Country, or Device Category.

• Metrics: These are the numbers you measure. They are the quantitative values you want to analyze. Examples include Sessions, Revenue, Conversions, Cost, or Click-Through Rate (CTR).

Your comparison chart will use a dimension to define what you are comparing (e.g., dates, campaigns) and a metric to define how you are measuring that comparison (e.g., by revenue, sessions).

Method 1: The Quick-and-Easy Scorecard Comparison

For a high-level, single-KPI snapshot, the scorecard is your best friend. This is perfect for dashboard headers that tell you essential information at a glance, like "Total Revenue this month vs. last month."

1. Add a Scorecard to Your Report

From the toolbar, select Add a chart > Scorecard. Place it on your report canvas.

2. Select Your Primary Metric

With the scorecard selected, use the Setup panel on the right. Under the "METRIC" section, choose the primary number you want to display. Let's use Total Revenue (or a similar metric from your data source) as an example.

3. Set the Default Date Range

Still in the Setup panel, find the "Default date range" section. This will determine the primary period for your data. You can set a custom range or use a preset like This Month or Last 30 days. Let’s select This Month.

4. Apply the Comparison Date Range

Here's where the comparison happens. Right below the "Default date range," you’ll see the "Comparison date range" field. Click on it and select one of the following:

• Previous period: This will compare your selection to the immediately preceding period of the same length. Since we chose "This Month," the previous period would be last month.

• Previous year: This option compares your metric to the same date range from the previous year. This is perfect for YoY analysis and accounting for seasonality.

Once you select "Previous period," you'll immediately see your scorecard update. It will now show the total revenue for this month, along with a percentage change and a small indicator showing the value from last month. It's an incredibly efficient way to get immediate context.

Method 2: Visualizing Trends with a Time Series or Bar Chart

While scorecards are great for KPIs, sometimes you need to see the entire trend over a period. Were sales consistently higher this month, or did one big spike account for the growth? A time series or line chart makes this clear.

1. Add a Time Series Chart to Your Report

From the toolbar, go to Add a Chart > Time Series chart and place it on your canvas.

2. Define Your Dimension and Metric

In the Setup panel, set your dimension and metric.

• For the Dimension, you'll almost always use a date field (e.g., Date).

• For the Metric, pick what you want to measure over time (e.g., Users).

3. Add a Comparison Date Range

Just like with the scorecard, scroll down to the "Comparison date range" section in the Setup panel. Select Previous period or Previous year.

Instantly, a second line will appear on your chart. The solid line represents the current period, while a lighter, often dashed line represents the comparison period. Now you can easily spot trends, divergences, and key moments where performance was stronger or weaker than the previous period.

Bonus Tip: Comparing Non-Date Categories with Bar Charts

What if you want to compare things that aren't dates, like ad campaigns? A bar chart is the way to go.

1. Add a Bar Chart to your report.

2. Set your Dimension to what you're comparing (e.g., Campaign Name).

3. Set your Metric to the value you're measuring (e.g., Conversions).

4. Use the Filter function at the bottom of the Setup panel to include only the specific campaigns you want to compare.

This will give you a clean side-by-side visualization of which campaign performed better based on your chosen metric.

Common Pitfalls and How to Avoid Them

Building comparison charts in Looker isn't always smooth sailing. Here are a few common issues and a little bit of advice for getting around them.

Problem: Comparing Data from Different Platforms

You want one chart showing conversions from Google Ads next to conversions from Facebook Ads. This is a common request, but it's tricky in Looker. The built-in connectors can't pull this data directly into the same chart. To solve this, you need to:

1. Export CSVs: Manually download your data from each platform.

2. Combine in Google Sheets: Aggregate the data into a single, well-structured Google Sheet. Make sure you have a common dimension, like Date or Campaign Type.

3. Data Blending: For a more advanced approach, you can use Looker Studio's data blending feature to join data sources. This involves connecting both sources to your report and creating a "blended data source" that joins them based on a common key (like the date). Be warned: blending can be complex and an easy place to make mistakes if your join keys aren't set up perfectly.

Either way, comparing data from entirely different ecosystems often requires manual data wrangling outside of Looker before you even begin building your chart.

Problem: Misleading Visualizations

A poorly chosen chart can tell the wrong story. When comparing website sessions (in the tens of thousands) against conversions (in the hundreds), putting them on the same axis on a line chart will make the conversion line look completely flat. In these cases, consider using a combo chart with two different Y-axes (one for sessions, one for conversions) or simply place two separate charts side-by-side.

Final Thoughts

Building comparison charts in Looker Studio is a powerful way to add essential context to your reporting. Whether you use simple scorecards for at-a-glance KPI monitoring or detailed time series charts to track daily trends, comparing data points is what transforms dashboards from data dumps into decision-making tools.

While Looker Studio is a fantastic tool once it’s set up, you can spend a lot of time connecting data, blending sources, and configuring charts. At Graphed, we built our tool because we believe getting these insights should be conversational, not manual. Instead of digging through menus to set a comparison date range, you simply ask, "Compare revenue from Facebook and Google Ads for the last 30 days" and the dashboard is created for you in seconds. We automate the entire process of connecting to your marketing and sales platforms, so you can stop wrestling with report builders and start asking your data the questions that matter.