In Excel: right-click the series with the different scale, choose Format Data Series and tick Secondary Axis — or use Chart Design ▸ Change Chart Type ▸ Combo and tick Secondary Axis next to that series.
On this page7
Build the chart with both series on it, even though one looks flat.
Click the flat series once to select it — if it is too small to hit, use Chart Design ▸ Select Data or the series dropdown on the Format tab.
Right-click ▸ Format Data Series ▸ Series Options ▸ Plot Series On ▸ Secondary Axis.
Open Chart Design ▸ Change Chart Type ▸ Combo and give the secondary series a different shape (usually Line) so the two are not mistaken for one scale.
Add an axis title on both sides stating the unit — a dual-axis chart without units is unreadable.
What this does
A secondary axis gives one series its own scale on the opposite side of the chart, so a small-magnitude series (a 4.2% conversion rate) stays visible next to a large-magnitude one (€480,000 of revenue). Without it the small series flattens into the baseline. Excel allows exactly one secondary axis per chart, and the Combo chart type is where you also choose a different shape — typically columns on the primary axis and a line on the secondary. Before you run it on a workbook other people depend on, try it on a copy or a few rows first. Undo only reaches back through the current session, so a quick trial run is the cheapest way to see exactly what will change before the file is saved and shared. For “excel chart two y axes”, the reliable version is a short checking loop, not just the first command that appears to work. Run it on a deliberately small range first, watch how the affected chart change, and only then apply the same setup to the full sheet. When this is a ribbon command, the selection matters more than the button: confirm the range, apply the command, then spot-check the output before saving. That is what makes a visual that makes the number obvious at a glance useful in real work: repeatable, auditable, and not dependent on memory or luck.
A worked example
B2:B13 holds monthly revenue (€40k–€90k) and C2:C13 holds conversion rate (3%–6%). Plotted together, the conversion line sits flat on zero. Right-click the conversion series ▸ Format Data Series ▸ Secondary Axis, then Change Chart Type ▸ Combo and set Revenue to Clustered Column and Conversion Rate to Line. Both curves are now readable, with % on the right axis. A secondary axis is what lets a rate sit beside a volume in one picture — revenue against margin, sessions against conversion, output against defect rate. When the result is not what you expected, undo straight away rather than repairing it by hand — undo restores the sheet exactly, while manual fixes tend to leave small inconsistencies behind that surface later.
In Google Sheets
This is a command rather than a formula, so there is no syntax to carry over. Google Sheets arranges its commands in menus across the top instead of a ribbon, names some of them differently and does not have every Excel command — look for the equivalent in the Sheets menus or its help before assuming the steps match. Keep this page bookmarked for the next time the same question comes up. Better still, repeat the steps once in your own workbook — doing it yourself is what turns a copied answer into something you remember. Treat “excel chart two y axes” as a routine rather than a one-off. Once you know which setting or command controls it, the same few steps handle every workbook where it comes up in Excel, and you can explain them to a colleague in a sentence.
Common mistakes
- Leaving both series as columns, so readers compare bar heights that use two different scales.
- Starting one axis at zero and the other somewhere else, which lets you manufacture an apparent correlation.
- Adding a secondary axis when the real fix is a percentage or index of both series on one scale.
- Forgetting the unit on the right-hand axis, the single most common reason a dual-axis chart gets misread.
Frequently asked questions
How do I add a secondary axis in Excel?
Right-click the series that needs its own scale, choose Format Data Series, and under Series Options select Secondary Axis. On Mac the same option sits in the Format Data Series pane.
Can a chart have two y axes?
Yes — one primary and one secondary, so two scales in total. Excel does not support a third.
Why is my secondary series invisible?
It is usually hidden behind the primary series. Change its chart type to Line under Change Chart Type ▸ Combo, or reorder the series in Select Data.
Is a dual-axis chart a good idea?
Only when the two series genuinely use different units. If both are currency or both are counts, one axis is clearer and harder to misread.