How to Make Double Y-Axis Graph in Google Sheets

Trying to compare two different types of data on a single graph, like website traffic and your much smaller conversion rate, can feel like an impossible task. This guide will walk you through exactly how to create a double y-axis graph in Google Sheets. You'll learn how to clearly visualize two metrics with different scales on one chart, making your reports much more insightful.

What is a Double Y-Axis Graph and Why Use One?

A double y-axis graph, also known as a dual-axis chart or combo chart, is a single chart that displays two y-axes (a left primary axis and a right secondary axis) to visualize two different types of data against the same x-axis.

So, when is this actually useful? Imagine you're a marketing manager looking at last month's performance. You want to see the relationship between your monthly ad spend (measured in thousands of dollars) and the number of leads generated (measured in hundreds).

If you plot both on a standard single y-axis chart, it might look something like this:

• The ad spend numbers are so large that they create a scale from $0 to $10,000.

• The number of leads, which might range from 50 to 250, becomes a nearly invisible flat line at the bottom of the graph.

The chart is technically accurate, but it's completely useless for analysis. You can't see the trends or fluctuations in your lead numbers because the scale is dominated by your ad spend. A double y-axis graph solves this by giving each dataset its own scale, allowing you to compare trends meaningfully.

Common scenarios for this type of chart include:

• Comparing revenue (large numbers) with profit margin (percentages).

• Visualizing website sessions (large numbers) against conversion rate (small decimals or percentages).

• Tracking sales volume (units) versus the average selling price (dollars).

Step 1: Preparing Your Data in Google Sheets

Before you can build your chart, you need to structure your data correctly. Thankfully, the format is simple and intuitive. You’ll need at least three columns:

• Column A: Your X-Axis. This is your independent variable, which is usually a dimension like time (Date, Month, Year).

• Column B: Your First Y-Axis Metric. This will be the data series that uses the left vertical axis.

• Column C: Your Second Y-Axis Metric. This is the data series you'll move to the right vertical axis.

For our example, let's say we're tracking monthly website sessions and the corresponding conversion rate for an e-commerce store. Your data should look like this:

Pro Tip: Make sure your numbers are formatted correctly. Percentages should be formatted as percentages (using the '%' button in the toolbar), and raw numbers should be general numbers. This helps Google Sheets create the axes accurately.

Step 2: Create a Basic Chart in Google Sheets

With your data prepped, creating the initial chart takes just a few clicks.

1. Click and drag to highlight the entire data range, including the headers (in our example, A1 through C7).

2. Navigate to the top menu and click Insert > Chart.

3. Google Sheets will automatically generate a default chart. It might try to guess and create a combo chart, but often it will create a simple line or column chart first. Don't worry, we'll fix this in the next step. A Chart editor pane will also appear on the right side of your screen.

Step 3: Assigning a Series to the Right Axis

This is where the magic happens. We're going to tell Google Sheets which data set should use its own, separate axis.

If Google didn't automatically select a Combo chart, you'll need to do it yourself first.

1. In the Chart editor > Setup tab, click the "Chart type" dropdown.

2. Scroll down to find the Combo chart option and select it. This chart type is specifically designed to handle mixed data series.

Now, let's move one of our metrics to its own axis.

1. In the Chart editor, click on the Customize tab.

2. Click on the Series dropdown to expand its options.

3. By default, the settings displayed are for your first data series (e.g., "Sessions"). You need to tell it which series you want to modify. Click the "Apply to all series" dropdown and select the series you want to move to the right axis (e.g., "Conversion Rate").

4. Below that, you will see a dropdown menu labeled Axis. Click it and select Right axis.

Instantly, you will see a new vertical axis appear on the right side of your chart, scaled perfectly for your "Conversion Rate" data. Now both sets of data are clearly visible and easy to compare.

Step 4: Customizing Your Chart for Readability

A basic double y-axis chart is good, but a well-customized one is great. Clear labels and distinct visuals prevent your audience from misinterpreting a complex chart.

Change Chart Types for Each Series

Mixing visual styles can make your combo chart even easier to read. A common and highly effective combination is using columns for one metric and a line for the other. This creates a clear visual distinction between the two datasets.

• Go back to the Customize > Series section of the Chart editor.

• Select your first data series (e.g., "Sessions"). Underneath "Color" and "Line dash type," you can confirm it's currently a "Columns" type.

• Now, switch to your second data series ("Conversion Rate"). In the type dropdown, you can change it from columns to Line. A line is perfect for showing a trend over time, especially for a metric like conversion rate.

Add Clear and Descriptive Axis Titles

A double y-axis chart is useless without clear titles. Your audience needs to know what each axis represents.

• In the Chart editor, head to Customize > Chart & axis titles.

• Select Vertical axis title from the dropdown and type in a new name (e.g., "Website Sessions").

• Next, select Right vertical axis title and give it a clear label (e.g., "Conversion Rate (%)").

• Don't forget the main chart title! Use the Chart title option to give it a descriptive name like "Website Sessions vs. Conversion Rate."

Adjust Colors and Scales

Finally, clean up the aesthetics for a professional looking finish.

• Colors: Under Customize > Series, you can assign different colors to each data series. Choose colors that have good contrast but aren’t jarring.

• Axis Scale: If you want to refine the scale of either y-axis (for example, starting the axis at a number other than zero), head to Customize > Vertical axis or Right vertical axis. Here you can set minimum and maximum values for stricter control over the visual.

Common Pitfalls and How to Avoid Them

Double y-axis charts are powerful, but they can also be misleading if used incorrectly. Keep these points in mind.

Mistake #1: Implying Causation

Just because you see two trends moving together doesn't mean one is causing the other. Your chart shows a correlation, not causation. For example, your sessions and conversion rate might both rise in May, but the rise in sessions didn't necessarily cause the improved conversion rate. A separate promotion or product launch could be influencing both.

Mistake #2: Overcluttered Visuals

It's tempting to add a third or fourth metric to the chart. Resist the urge. A combo chart is most effective with just two data series. Any more, and it becomes a confusing mess of lines and bars that is almost impossible to interpret.

Mistake #3: Missing Axis Labels

Never leave your axes unlabeled. This is the surest way to confuse whoever is reading your report. It’s absolutely critical that each axis is clearly and unambiguously labeled so the viewer understands which scale applies to which data.

Final Thoughts

Creating a double y-axis graph in Google Sheets is a straightforward process that can turn a confusing dataset into a powerful, insightful visual. By organizing your data correctly and methodically using the chart editor, you can effectively compare two completely different metrics on a single, easy-to-read chart.

Manually preparing data and building reports like this every week can be time-consuming. At my company, we built Graphed to remove this manual work entirely. We connect directly to your data sources like Google Analytics, Shopify, and your ad platforms. Instead of building charts click-by-click, you can just ask a question like, "Show me a chart of my website sessions versus the overall conversion rate by month," and Graphed builds a live, interactive dashboard for you instantly.