When you need a second vertical axis

A second vertical axis in Excel lets you plot two data series that use completely different scales on the same chart. If you're charting monthly revenue alongside customer count, or temperature alongside humidity, the numbers are so far apart that one series flattens against the bottom while the other shoots off the top. A second axis solves this by giving each series its own scale.

The second axis is not decorative — it's the only way to see the actual relationship between two measurements that don't share a unit or magnitude. Without it, a chart with revenue in the millions and customer count in the hundreds becomes unreadable.

Key Takeaways

  • Right-click the data series with the smaller or different-scale numbers, then select "Format Data Series" and choose "Secondary Axis" to move it to a new vertical axis.
  • The second axis appears on the right side of the chart and uses its own scale, independent of the left axis.
  • You can format each axis separately — change the number format, minimum and maximum values, and gridlines for each one.
  • A second axis works best when you have exactly two data series; more than that becomes confusing even with multiple axes.

The step-by-step process

Start with a chart that already contains both data series. Select the chart by clicking it once. The chart border will show selection handles around the edges.

Right-click directly on the data series you want to move to the second axis — the line, bars, or points themselves, not the background. A menu will appear. Click "Format Data Series" (or "Format Data Point" if you right-clicked a single point). A panel will open on the right side of your screen.

In the Format Data Series panel, look for the "Series Options" tab (it looks like a bar chart icon). Scroll down until you see "Plot Series On" with two radio buttons: "Primary Axis" and "Secondary Axis". Click "Secondary Axis". Close the panel. The chart will redraw with the second axis on the right side, and your selected series will now use that new scale.

Reading and adjusting the two axes

After you add a second axis, your chart now has two vertical scales. The left axis still shows the scale for your first data series. The right axis shows the scale for the series you moved. Each axis is independent — changing one does not affect the other.

To adjust either axis, right-click on the axis numbers themselves (not the data). Select "Format Axis". A panel opens where you can change the minimum value, maximum value, number format, and decimal places. For example, if your left axis shows revenue in dollars and displays values like 1000000, 2000000, you can format it to show 1M, 2M instead. The right axis can use a completely different format.

You can also add or remove gridlines for each axis separately. In the Format Axis panel, look for "Gridlines" and toggle them on or off. This helps readers see which values correspond to which axis.

Labeling your axes so readers understand them

With two axes, your chart needs clear labels or readers will misread it. Click the chart once to select it. Go to the "Chart Design" tab in the ribbon at the top. Click "Add Chart Element", then "Axis Titles", then "Primary Vertical" to add a label to the left axis. Type a name like "Revenue ($)" or "Temperature (°F)".

Repeat the process for the secondary axis: click "Add Chart Element", then "Axis Titles", then "Secondary Vertical". Type the label for the right axis, such as "Customer Count" or "Humidity (%)".

You should also add a chart title that makes clear you're comparing two different measurements. Something like "Monthly Revenue vs. Customer Count" tells the reader when ready what they're looking at.

Common mistakes to avoid

The most common error is forgetting to label the axes. A reader will assume both axes use the same scale and draw the wrong conclusion. Always add axis titles and a descriptive chart title.

Another mistake is using a second axis when you should use two separate charts instead. If your two data series have no relationship to each other — if you're not trying to show how they move together — two side-by-side charts are clearer than one chart with two axes. A second axis implies you want readers to compare the trends, so use it only when that comparison matters.

Do not add more than two axes. Excel allows it technically, but three or more axes make a chart nearly impossible to read. If you need to show three or more unrelated measurements, use multiple charts or a different visualization.

Changing the axis type or removing the second axis

If you change your mind and want to move a series back to the primary axis, right-click the series again, select "Format Data Series", go to "Series Options", and click "Primary Axis".

To delete the second axis entirely, right-click on the axis numbers on the right side of the chart and select "Delete". The axis disappears, but the data series stays — it will now use the primary axis scale, which may make it hard to see. You can then adjust the primary axis scale to fit both series, or delete the series that no longer fits.

When a secondary axis is not the answer

A second axis works when you have two series with genuinely different scales that you want to compare. It does not work when your data is incomplete, when one series is much more volatile than the other, or when the two measurements have no logical connection.

If one series has huge swings and the other is nearly flat, a second axis can make the flat series look more dramatic than it actually is. Readers may think the two are more closely related than they are. In that case, consider showing them in separate charts with their own scales, or using a different chart type like a combo chart that mixes bars and lines.

Frequently Asked Questions

Can I use a second axis with a bar chart?

Yes. Right-click the data series you want to move, select "Format Data Series", go to "Series Options", and click "Secondary Axis". The process is the same as with line or area charts. You may want to change one series to a different chart type (like bars on the left and a line on the right) to make the difference clear.

What if my second axis scale looks wrong or backwards?

Right-click the axis numbers on the right side, select "Format Axis", and check the "Axis Options" section. You can set the minimum and maximum values manually, or check the "Categories in reverse order" box if the scale is inverted. Make sure the scale makes sense for your data.

How do I make the second axis more visible?

Right-click the axis numbers on the right, select "Format Axis", and look for "Line" options. You can change the line color or thickness. You can also add axis labels and a title to make it stand out. Some people use a different color for each axis to help readers match the axis to the data series.

Can I have different chart types on each axis?

Yes. After adding the second axis, right-click the series on the secondary axis and select "Change Series Chart Type". Choose a different type — for example, bars on the primary axis and a line on the secondary axis. This makes it visually clear that you're showing two different things.

What if both my data series have the same scale?

Then you do not need a second axis. A second axis is only useful when the two series use different units or have very different ranges. If they use the same scale, a single axis is clearer and less likely to confuse readers.