How to Add a Secondary Axis in Excel

Excel's charts give you a variety of ways to visualize your data. For charts that utilize an X-and-Y-axis layout, you have the ability to view a series of data, which allows you to compare two different things, but those things will usually have the same unit of measure. In this article, we'll show you how adding a secondary axis to Excel allows you to view unlike things on the same graph.

When You Should Use a Secondary Axis in Excel

As mentioned, secondary axis are used to compare two things that don't have the same unit of measure.

Consider the above example, where we're looking at a company's revenue versus its expenses for the last five years. Both of these are measured in dollars, so we can set up a line graph showing both of these in the same view to determine the relationship.

As you can see in the above screenshot, the y-axis on the left is displaying the USD units, but what if you want to see if there's a similar trend as it pertains to costs and employees? The unit for Employees is people, not dollars, so you can't very well use the existing y-axis. This is where you should add a second axis to ensure your reader can accurately understand what the numbers mean.

A second reason is when the two series don't have data in the same magnitude. Consider, for example, the revenue of the company versus the employees. The chart above shows that when visualized together it doesn't provide much insight, because the number of employees is so low you can't determine what's happening with it.

Instead, you can add a second axis that has both its own units as well as its own scale, allowing you to really compare the two.

How to Add a Secondary Axis in Excel

1. First, select the line (or columns, etc.) associated with the second data series.

2. By selecting an element on a chart, the Chart Tools tab will appear in the ribbon.

3. Select the Format tab.

4. To the far left, the Current Selection box should already display the series you selected. In this example, it's Series "Employees."

5. Select Format Selection.

6. Now, in the right-hand panel, under Series Options, select Secondary Axis.

7. Once added, this second axis can be customized just like the primary axis. You can change the text alignment or direction, give it a unique axis label, or modify the number format.

8. Now look at your chart. The secondary axis will appear on the right side, and Excel will even take some default guesses regarding scale. Compared to the first version of this chart, adding a second axis makes it much easier to compare the trends.