How to Overlay Graphs in Google Sheets

Trying to show how your ad spend influences website traffic on a single Google Sheets chart can quickly become a mess. One set of numbers is in the thousands, the other is in the hundreds, and when you plot them together, one line just looks like a flat line at the bottom. This article will show you exactly how to solve that by overlaying graphs, creating a single, clear visual that tells the whole story.

Why Fusing Graphs Together is So Powerful

Before jumping into the "how," it’s important to understand the "why." Overlaying graphs isn’t just a cool spreadsheet trick, it helps you uncover insights that are much harder to see when looking at separate charts. It turns flat numbers into a compelling data story.

The main goals of overlaying graphs are:

• Comparing Trends Over Time: Did website conversions really go up after we started that new email campaign? By placing email sends and conversion numbers on the same timeline, you can visually connect the dots between your actions and their results.
• Showing Correlation: This is the classic use case. You want to see if two different metrics move together. For instance, plotting monthly revenue (as columns) and ad spend (as a line) on the same chart can immediately show if higher spending periods correspond with higher revenue.
• Visualizing Targets vs. Actual Performance: One of the best ways to track goals is to plot your target (as a straight or dashed line) across a chart showing your actual performance (as columns or a solid line). This gives you an instant progress report that a simple table of numbers can’t provide.

The Simplest Method: The Combo Chart

Google Sheets has a specific tool for this exact task: the Combo Chart. A combo chart is just what it sounds like - it combines two different chart types into a single graph. The most common and effective combination is a column chart and a line chart.

This approach allows you to represent two different types of data cleanly. For example, you can use columns to represent a quantity or volume (like sales or website sessions) and a line to represent a continuous metric (like cost, average conversion rate, or temperature).

Let's build one from scratch.

Step-by-Step: How to Overlay Graphs with a Combo Chart

We're going to use a common marketing scenario: analyzing the relationship between monthly ad spend and website sessions. You want to see if spending more money is actually driving more people to your site.

Imagine this is your data:

Step 1: Get Your Data Organized

The success of your chart depends entirely on how your data is structured. Before you even think about creating a chart, make sure your data table is clean and simple. Here are the rules:

• Your first column should be your shared x-axis label. In our case, this is the Month. This is most often a time-based metric (day, week, month, quarter).
• The subsequent columns should contain the numeric data you want to plot. Here, that's Website Sessions and Ad Spend.
• Every column must have a clear header. These headers will automatically become the labels for your data series.

Clean data is the foundation of a good chart. Spending 30 seconds to organize your spreadsheet will save you minutes of frustration in the chart editor.

Step 2: Highlight Your Data and Insert the Chart

Click and drag your cursor to highlight the entire data range, including the headers (from cell A1 to C7 in our example).

Go to the main menu and click Insert > Chart. Google Sheets will take its best guess at the right chart type, often giving you a bar chart or line chart by default. Don't worry if it doesn't look right yet, we'll fix that in the next step.

Step 3: Change to a Combo Chart

With the Chart editor pane open on the right, navigate to the "Setup" tab. Click on the dropdown menu under "Chart type" and scroll down to the "Combo chart" option. It's usually found between the Line and Area chart sections.

As soon as you select it, your chart will update to show both columns and a line. But you'll probably notice a big problem immediately: the "Ad Spend" line is nearly flat at the very bottom of the chart. This happens because the scale for "Website Sessions" (in the tens of thousands) is so much larger than the scale for "Ad Spend" (in the hundreds or low thousands), making the Ad Spend values look tiny in comparison.

This is the most common pitfall people face, but it has a simple fix.

Step 4: Add a Secondary Axis to Fix the Scale

To make both data series readable, we need to assign one of them to its own vertical axis. This is the single most important step for overlaying graphs with different scales.

1. In the Chart editor, click on the Customize tab.
2. Click to expand the Series section. This is where you can format each individual data series.
3. You'll see a dropdown menu that says "Apply to all series." Click on it and select the series you want to move to its own axis. In our case, that’s Ad Spend ($).
4. Once you’ve selected "Ad Spend ($)," you will see formatting options for it. Look for the "Axis" dropdown, which is set to "Left axis" by default. Click it and change it to Right axis.

Instantly, a new vertical axis appears on the right side of your chart, scaled specifically for the Ad Spend data. Your once-flat line will now have its own defined shape, making the relationship between the two datasets perfectly clear.

Step 5: Polish and Finalize Your Chart

Your chart is now functional, but a little bit of polish makes it more professional and easier to understand. Here are a few recommended tweaks in the Customize tab:

• Chart & axis titles: Give your chart a descriptive title, like "Website Sessions vs. Ad Spend." Then, go to "Vertical axis titles" and label both the left ("Website Sessions") and right ("Ad Spend in $") axes so a viewer knows what each scale represents.
• Colors and Styles: Under the "Series" section, you can change the color of your columns and line to match your branding or make them visually distinct. You can also adjust the line thickness or change the line to be dashed.
• Legend: Make sure the legend is clear and positioned well (top or bottom is usually best). This helps viewers instantly associate each visual element with its metric.

Now you have a professional-looking combo chart that clearly shows the relationship between your two key metrics.

Advanced Scenarios and Tips

Comparing More Than Two Metrics

A combo chart isn't limited to just two data series. For example, you could add a "Conversions" column to your data and add it as a second line on your chart. Just be careful not to make the chart too crowded. A good rule is to stick to one set of columns and one or two lines to keep it readable.

Plotting Performance Against a Goal

Let's say your monthly sales goal is $25,000. You can add a column to your data called "Sales Goal" and fill every row with "25000." Plot your actual sales as bars and the goal as a dashed line on the same chart. This gives your team a clear view of where they stand each month.

Final Thoughts

Creating a combo chart is the most effective way to overlay graphs in Google Sheets. Once you get the hang of setting up your data and using the secondary axis, you can craft compelling visualizations that reveal trends and correlations you might have otherwise missed. It’s a powerful skill for anyone looking to make better sense of their data.

Of course, the most tedious part of this process is often getting all your data in one place - like pulling session data from Google Analytics and cost data from each of your ad platforms. It’s a lot of manual downloading and copy-pasting. That's actually why we built our platform. With Graphed , you can securely connect multiple data sources like Google Analytics and Facebook Ads, and then simply ask for the chart you want in plain English. For example, you could ask, "Show me a dashboard comparing Facebook Ads spend vs. GA4 sessions as a combo chart for the last six months," and have it built for you in seconds, no spreadsheet wrangling required.