How to Add Secondary Axis in Power BI

Adding a secondary axis to a chart in Power BI lets you compare two different types of data on a single visual, which is perfect for telling a more complete story about your business performance. This guide will walk you through exactly how and when to use a secondary axis to make your reports clearer and more insightful.

When to Use a Secondary Y-Axis in Your Reports

A secondary Y-axis is most useful in a few key scenarios. The general rule is to use one when you need to plot two different data measures that have drastically different scales or units of measurement.

Imagine you’re tracking your company's monthly revenue and the number of units sold. Your revenue is in the millions of dollars, while the units sold are in the tens of thousands. If you plot both on the same Y-axis, the "Units Sold" line will appear as a flat, insignificant line at the very bottom of the chart, completely dwarfed by the massive revenue figures. It's impossible to see any trends in unit sales.

By adding a secondary axis, you give each measure its own scale. Revenue might use the primary axis on the left (scaled in millions), while Units Sold uses the secondary axis on the right (scaled in thousands). Now, both trends are clearly visible and can be compared side-by-side.

Common Scenarios for a Secondary Axis:

• Comparing Money and Volume: Plotting Sales Revenue ($) against Units Sold or Marketing Ad Spend ($) against Website Clicks.
• Mixing Absolute Numbers and Percentages: Tracking Total Sales ($) against Profit Margin (%), where one is a large number and the other is a small percentage.
• Showing Correlation or Causation: Visualizing how your email campaign sends (count) relate to website traffic (sessions) or how customer support tickets (count) relate to customer satisfaction scores (%).

Basically, if putting two metrics on the same axis makes one of them unreadable, a secondary axis is your solution.

How to Create a Combo Chart with a Secondary Axis

In Power BI, the visual that supports a secondary axis is called a "combo chart." You have two primary options: the Line and stacked column chart or the Line and clustered column chart. Let's walk through creating one step-by-step using a classic example: comparing Sales Revenue with Profit Margin percentage over time.

Step 1: Select the Combo Chart Visual

Start by adding the right visual to your report canvas.

1. On the Power BI report canvas, navigate to the Visualizations pane on the right side of your screen.
2. Find the icon that looks like a bar chart with a line graph superimposed on it. Click on either the “Line and stacked column chart” or the “Line and clustered column chart.” For this example, we’ll use the clustered column chart.

Step 2: Add Your Data to the Visual's Fields

Once you have the visual on your canvas, you need to populate it with your data. With the visual selected, look at the Visualizations pane again. You’ll see several data “wells” where you can drag and drop fields from your Data pane.

• Shared X-axis: This is your common dimension, what you’re measuring across. Typically, this is a time period like Date, Month, or Year. Drag your Date or Month field here.
• Column Y-axis: This will be your primary metric displayed as columns. Let’s use Sales Revenue. Drag it to this well.
• Line Y-axis: This is the metric you want to show as a line and eventually move to the secondary axis. Drag your Profit Margin field here.

Step 3: Activate the Secondary Y-Axis

This is where the magic happens. We'll tell Power BI to move the line chart metric to its own axis.

1. With your combo chart selected, click the “Format your visual” icon in the Visualizations pane (it looks like a paintbrush).
2. Scroll down and expand the "Secondary Y-axis" section.
3. Simply toggle the switch to On.

Instantly, a new axis will appear on the right side of your chart, scaled specifically for your line chart data (Profit Margin). Your Profit Margin line will now have its own scale and will show its trend clearly, independent of the scale used for Sales Revenue.

Tips for Customizing Your Combo Chart

Just creating the chart is half the battle. To make it truly professional and easy to understand, you'll want to spend a few minutes customizing it in the “Format your visual” pane.

Label Your Axes Clearly

With two Y-axes, clear titles are mandatory to avoid confusion. By default, Power BI might show titles like "Sum of Sales Revenue." Make them cleaner and more intuitive.

• Go to the “Format your visual” pane.
• Under Y-axis, find the Title section and change the Text to something clean like "Sales Revenue."
• Do the same for the Secondary Y-axis, changing its title text to "Profit Margin %."
• While you're at it, give your visual a descriptive title in the General > Title section, like "Monthly Sales Revenue vs. Profit Margin."

Adjust Colors for Clarity

Making your visual easy on the eyes helps convey information more effectively. Pick colors that have enough contrast to be easily distinguished.

• Under Visual, expand the Columns section and choose a color for your Sales Revenue bars.
• Expand the Lines section and choose a contrasting color for your Profit Margin line. A solid, muted color for the columns (like dark blue or gray) combined with a brighter line color (like orange or light green) often works well.

Turn on Data Labels and Markers

Sometimes you need to see the exact values without hovering over every point. Data labels help with this.

• Go to the Data labels section and turn them On.
• A sub-menu will appear where you can specify which series to apply labels to (all, columns, or line). You can customize the font, size, and position for each.
• In the Lines formatting section, you can turn on Markers to add a shape (circle, square, etc.) to each data point on the line, making it easier to track.

Best Practices (and What to Avoid)

Secondary axis charts are powerful, but they can also be misleading if used incorrectly. Follow these best practices to ensure your visuals are clear, honest, and effective.

• Keep it Simple: While you technically can add more lines or columns, a dual-axis chart is most effective with just two metrics—one for the columns and one for the line. Adding more can quickly turn a clear visual into a cluttered "spaghetti chart" that’s impossible to read.
• Ensure Context: Make sure the two metrics you're comparing have a logical relationship. Plotting "Website Traffic" against "Office Coffee Consumption" probably doesn't make sense. Plotting "Ad Spend" against "New Leads" does.
• Label Indisputably: We mentioned this before, but it bears repeating. Anyone looking at your chart should immediately understand what the bars represent, what the line represents, what the left axis measures, and what the right axis measures. Use clear, simple titles everywhere.
• Be Careful With Zero Baselines: A common critique of dual-axis charts is that they can manipulate perception. For example, if your revenue grew from $10M to $11M (a 10% increase) but your user base grew from 100 to 500 (a 400% increase), you could adjust the axes to make the revenue growth look much steeper than the user growth. When possible, keep your axes baselines at zero, especially for column charts. An exception is often made for metrics where zero is not a meaningful baseline, like temperature or stock prices. Use your best judgment to present the data honestly.

Final Thoughts

Mastering the secondary Y-axis in Power BI is a great skill that elevates your reports from simple data dumps to compelling visual stories. It allows you to elegantly display relationships between two distinct metrics, providing nuanced insights that a single-axis chart could never show.

Of course, building dashboards in tools like Power BI still involves a lot of clicking, dragging, and formatting. Manually building reports—especially when you need to combine data from different platforms like Google Analytics, Shopify, and your CRM—can eat up hours. With tools like Graphed you can automate that entire process. You can simply connect your data sources in a few clicks and ask in plain English, "Create a chart showing Shopify revenue vs. Facebook ad spend by month," and get a live, interactive dashboard in seconds, with no need to manually configure fields or axes at all.