What a secondary axis does and when you need one
A secondary axis in Excel lets you plot two data series on the same chart even when they use different scales or units. If you're charting sales revenue alongside customer count, or temperature alongside humidity, the numbers are so different that one series flattens against the bottom while the other shoots off the top. A secondary axis gives the second series its own scale on the right side of the chart, so both become readable.
You add a secondary axis by selecting the data series you want to move, then changing its axis assignment in the chart formatting menu. Excel handles the scaling automatically — the secondary axis adjusts to fit the range of that series' values. The result is a chart where both lines or bars are visible and meaningful, even though they measure completely different things.
Key Takeaways
- A secondary axis appears on the right side of the chart and has its own scale, letting you plot two data series with different units or ranges on one chart.
- To add a secondary axis, right-click the data series you want to move, select "Format Data Series", and change the "Plot Series On" setting from Primary Axis to Secondary Axis.
- The secondary axis scale adjusts automatically to fit the values in that series, so you do not have to set minimum or maximum values yourself.
- You can format the secondary axis independently — change its title, number format, or scale — without affecting the primary axis.
Steps to add a secondary axis to an existing chart
Start with a chart that already contains both data series. Click on the chart to select it, then click on the specific data series you want to move to the secondary axis. In Excel, you click once to select the chart, then click again on the series itself — you'll see small squares appear on each data point when the series is selected.
Right-click the selected series and choose "Format Data Series" from the menu. In the Format Data Series pane that opens on the right side of the screen, look for the "Series Options" section. You'll see a setting called "Plot Series On" with two radio buttons: "Primary Axis" and "Secondary Axis". Click the "Secondary Axis" button. Close the pane, and Excel will redraw the chart with that series on a new axis on the right side.
How to add axis titles so readers know what each scale measures
Once the secondary axis appears, add a title to it so viewers understand what the right-side scale represents. Click the chart, then go to the Chart Design tab in the ribbon at the top. Click "Add Chart Element", then hover over "Axis Titles" and select "Secondary Vertical". A text box will appear on the right side of the chart where you can type the name of that axis — for example, "Customer Count" or "Humidity %".
You can also add or edit the primary axis title the same way. Go to Chart Design, Add Chart Element, Axis Titles, and select "Primary Vertical". Both axis titles help anyone reading the chart understand what each scale measures and why they're different.
Formatting the secondary axis scale and labels
If the secondary axis scale doesn't look right — if the numbers are too crowded, or the range doesn't match your data well — you can adjust it. Right-click the secondary axis itself (the numbers on the right side of the chart) and select "Format Axis". A pane opens where you can set the minimum value, maximum value, and major unit (the spacing between tick marks).
You can also change the number format here. If the secondary axis is showing decimal places you don't need, or if you want to add a percent sign or currency symbol, the number format dropdown lets you choose from built-in formats or create a custom one. These changes affect only the secondary axis — the primary axis on the left keeps its own formatting.
Switching a series back to the primary axis
If you move a series to the secondary axis by mistake, or if you later decide the chart layout should change, you can move it back. Click the chart, then click the series on the secondary axis to select it. Right-click and choose "Format Data Series", then click the "Primary Axis" radio button under "Plot Series On". The series moves back to the left axis immediately.
You can also use this method to move series back and forth as you experiment with different chart layouts. If you move the last series off the secondary axis, Excel removes the secondary axis automatically.
Common chart types that work with secondary axes
Secondary axes work best with column, bar, line, and area charts. You can mix chart types too — for example, show one series as columns on the primary axis and another as a line on the secondary axis. This combination is useful when you want to emphasize different aspects of the data: columns might show total sales, while a line shows profit margin.
Pie charts and doughnut charts don't support secondary axes because they don't use a traditional x-y layout. Scatter plots can use secondary axes, but they're less common because scatter plots usually compare two related measurements that benefit from the same scale.
Troubleshooting secondary axis problems
If the secondary axis doesn't appear after you select "Secondary Axis", make sure you clicked on the data series itself, not the chart background. The series must be selected — you should see small squares on each data point. If you see a message that says the axis can't be added, the chart type you're using may not support secondary axes.
If the secondary axis scale looks wrong — for example, if one series is still flattened against the bottom — check that you selected the correct series. It's easy to accidentally select the wrong one if the chart is crowded. Click once on the chart, wait a moment, then click directly on the line or bar you want to move. If the scale still doesn't look balanced, you can manually adjust the minimum and maximum values in the Format Axis pane to spread the data across more of the chart area.
Frequently Asked Questions
Can I add more than one secondary axis?
No. Excel charts support only one primary axis and one secondary axis. If you need to plot three or more series with different scales, you'll have to choose which two are most important and put the others on the same axis, or create separate charts.
Does the secondary axis have to be on the right side?
Yes. The secondary axis always appears on the right side of the chart in Excel. You cannot move it to the top, bottom, or left. If you need the secondary axis on a different side, you would have to create the chart in a different tool or manually rearrange the data.
What happens to the secondary axis if I delete the series on it?
Excel removes the secondary axis automatically when you delete the last series assigned to it. If you have two series on the secondary axis and delete one, the other series stays on the secondary axis and the axis remains visible.
Can I change the color of the secondary axis?
Yes. Right-click the secondary axis (the numbers on the right side), select "Format Axis", and look for the "Line" section in the pane. You can change the color, width, and style of the axis line itself. You can also format the text color and size of the axis labels separately.
Why does my secondary axis show negative numbers when my data is all positive?
This usually happens when Excel's automatic scaling sets the minimum value below zero. Right-click the secondary axis, select "Format Axis", and under "Bounds" set the minimum value to 0 or to the lowest value in your data. This forces the axis to start at a sensible point.