How to Merge Axis in Tableau

Trying to show two different metrics on the same chart in Tableau can feel tricky, but it's one of the most powerful ways to tell a story with your data. The key is to create a dual-axis chart, which allows you to overlay two different sets of data, even if they have completely different scales - like sales in dollars and shipping volume in units. This guide will walk you through exactly how to merge axes in Tableau, moving from two separate charts to one insightful, combined view.

What is a Dual-Axis Chart?

A dual-axis chart in Tableau is a single chart that features two independent axes, one on the left and one on the right. This setup is perfect for visualizing the relationship between two different measures against the same dimension. For example, you might want to compare your monthly marketing spend (in dollars) with the number of new website sign-ups (a count) over the same time period.

Each axis can be customized independently, allowing each measure to have its own mark type (bar, line, shape, etc.). This flexibility is what makes it possible to overlay a line chart on top of a bar chart, creating what's often called a "combo chart."

Common Use Cases for Merging Axes:

Comparing Measures with Different Scales: Plotting revenue (millions of dollars) and profit ratio (a percentage) on the same chart.
Showing Correlation: Visualizing how customer support tickets (a count) fluctuate with website traffic (number of sessions).
Creating Combo Charts: Displaying total sales as bars and the average deal size as a line to see how they trend together over time.
Contextualizing Data: Showing advertising spend as a line over a bar chart of monthly leads to quickly assess the effectiveness of your campaigns.

How to Merge Axes in Tableau (Step-by-Step Guide)

Let's walk through a common business scenario. Imagine you want to see the relationship between your monthly sales figures and the quantity of items sold. Sales will be a large dollar value, while quantity will be a smaller whole number. A dual-axis chart is the perfect solution.

For this example, we'll use Tableau's sample "Superstore" dataset.

Step 1: Build Your Initial View

First, create a simple line chart showing sales over time. This will form the foundation of our combo chart.

Drag the "Order Date" dimension to the Columns shelf. Right-click the "Order Date" pill and select "Month" (the second, continuous option, often shown as MONTH(Order Date)). This gives us a continuous time axis.
Drag the "Sales" measure to the Rows shelf.

You should now see a single line chart showing your total sales for each month.

Step 2: Add the Second Measure

Now, let's bring in the second piece of data we want to analyze. We want to see the quantity of items sold alongside the sales revenue.

Drag the "Quantity" measure from the Data pane and drop it onto the Rows shelf, to the right of the "SUM(Sales)" pill.

Tableau will automatically create a second line chart directly below the first one. You'll now have two separate charts in your view, each with its own Y-axis (one for Sales, one for Quantity).

Step 3: Create the Dual Axis

This is where the magic happens. We'll tell Tableau to merge these two charts into a single space by using a second, right-hand axis.

On the Rows shelf, find the "SUM(Quantity)" pill you just added.
Right-click the pill and select "Dual Axis" from the dropdown menu.

Instantly, Tableau combines the two charts. You'll see the "Sales" axis on the left and the "Quantity" axis on the right. Tableau might have automatically changed the mark type for both into circles, but we'll fix that next.

Step 4: Adjust Mark Types

A combo chart is most effective when the two measures have different visual forms, like bars and a line. This makes the chart much easier to read. Notice that in your Tableau workbook, the Marks card has changed. You now see tabs for "All," "SUM(Sales)," and "SUM(Quantity)," allowing you to control each measure's visualization independently.

Click on the "SUM(Sales)" Marks card.
In the dropdown menu that currently says "Automatic," select "Bar". Your sales data will now appear as a bar chart.
Next, click on the "SUM(Quantity)" Marks card.
In its dropdown menu, select "Line".

You've now successfully created a combo chart! It displays your sales as vertical bars and the quantity sold as a line overlaid on top, allowing you to easily compare their monthly trends in a single, unified view.

Don't Forget to Synchronize Your Axes (When It Makes Sense)

Synchronizing axes is a crucial step that ensures both axes use the same scale. This is essential when you're comparing two measures that are in the same unit of measurement (e.g., Sales vs. Profit, both in dollars) because it creates an apples-to-apples comparison.

If you plotted "Target Sales" and "Actual Sales" without synchronizing, the lines might look identical even if the actual performance was far below the target, which would be misleading.

How to Synchronize Axes:

Move your mouse over the right-hand axis (in our example, a "Quantity" axis) until the cursor changes.
Right-click the axis.
Select "Synchronize Axis" from the menu.

Important Note: In our example of Sales ($ thousands) vs. Quantity (hundreds), synchronizing the axes wouldn't make sense. The sales numbers are so much larger than the quantity figures that the 'Quantity' line would be flattened near the bottom of the chart, providing no insight. Only synchronize axes when the measures are directly comparable and share the same unit.

Best Practices for Using Dual-Axis Charts

Merging axes is a powerful technique, but it can create confusing visualizations if not used carefully. Here are a few tips to keep your charts clean and easy to interpret.

Use Different Colors: Assign distinct, logical colors to each measure. For instance, use a strong color like blue for your primary measure (e.g., Sales) and a contrasting accent color like orange for the secondary line (e.g., Quantity). This helps differentiate the data series at a glance.
Keep it Simple: Dual-axis charts are great for two measures. Attempting to add a third or fourth measure often results in a cluttered and unreadable chart. If you need to compare more than two metrics, consider creating separate charts in a dashboard instead.
Label Your Axes Clearly: Make sure both the left and right axes have descriptive titles. This helps your audience understand exactly what each scale represents without having to guess.
Provide a Legend: Tableau often creates a legend automatically, but make sure it’s visible and easy to understand. You can edit the legend titles to be more descriptive than default measure names (e.g., change "SUM(Sales)" to "Total Monthly Sales").

Final Thoughts

Learning how to merge axes in Tableau unlocks a new level of data visualization, allowing you to create rich, comparative charts that tell a complete story. By mastering the dual-axis feature, adjusting mark types, and understanding when to synchronize your axes, you can build powerful combo charts that highlight key relationships between different parts of your business.

Perfecting complex visualizations in tools like Tableau takes practice, involving many clicks, drags, and configurations to get just right. We built Graphed because we believe getting insights shouldn’t always require so much manual work. It lets you use plain English to describe the chart you need - like "show me sales as bars and quantity sold as a line chart by month" - and instantly builds the dashboard for you, connecting directly to live data sources without the step-by-step assembly.