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.
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. Keep the inputs visible and clearly labelled and the whole thing stays auditable — anyone who opens the file later, including you, can see at a glance exactly what feeds the result and change one assumption without hunting through the formula. For “two y axes in excel”, 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 axis 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 text operation that turns messy entries into clean, usable data 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. A practical tip before you scale it up: build it once on a small block of test data, confirm the number against the tool on this page, and only then point it at your real sheet. That one habit catches almost every mistake while it is still cheap to fix, long before a wrong figure reaches a report or a colleague.
In Google Sheets
If you are in Google Sheets rather than Excel, the good news is that the formula shown here is identical and the workflow barely changes — menus sit across the top instead of in a ribbon, and a few function names differ slightly, but anything you build here moves across with little or no rework. Keep this page bookmarked for the next time the same question comes up. Better still, rebuild the example once in your own sheet — doing it yourself, with the tool above to check against, is what turns a copied formula into a technique you own. Here is the takeaway for “two y axes in excel”: copy the answer if you are busy, but if you have a spare few minutes, rebuild the example in Excel yourself with the tool above open beside it. That single pass — type it, run it, watch the result move when you change an input — is what turns a formula you found into a technique you trust. Keep your inputs labelled and referenced, never hard-coded, and the same sheet stays correct and auditable as it grows. Done that way, you will not need to look this up again, and you will be the person others ask.
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.