Build a Google Sheets Combo Chart Without Misleading Scales

Quick answer

Use a combo chart when different series genuinely need different representations, not simply to make one line look steeper. Google’s combo chart reference documents column/line combinations and per-series axis assignment. This exercise uses count columns and a rate line, with their units made explicit.

This is a computer-browser workflow for an editable native spreadsheet. The public help is a rolling service reference, not a tested build or an account-entitlement guarantee. No sign-in, paid trial, application screenshot or native rendering was performed. The fixture and numeric checks below are original and independently calculated outside Sheets.

Prepare counts and rates separately

Enter this invented packing-quality dataset in A1:D5. Type the rates as percentages, including the percent sign.

Period	Packed boxes	Inspection pass rate	Inspected boxes
Week 1	80	90%	20
Week 2	120	95%	40
Week 3	100	80%	10
Week 4	160	100%	30

Columns B and D measure different populations. The pass rate describes inspected boxes, not all packed boxes. Keep D for checking the rate, but exclude it from the chart in this lesson. The chart range is A1:C5.

Expected controls:

• Packed boxes total 460.
• Inspected boxes total 100.
• Passing inspections by week are 18, 38, 8, 30, or 94 altogether.
• The combined inspection pass rate is 94%, not the simple average of the weekly percentages, 91.25%. The weekly denominators differ.

These totals are checks, not additional chart rows. Put any check formulas outside the plotted range. For example, =SUM(B2:B5) should return 460. A displayed 90% represents 0.9, not 90; entering 90 and then applying percentage formatting would represent 9000%.

Create and assign the two series

Select A1:C5 and choose Insert → Chart. Double-click the chart, then use Setup → Chart type to select a combo chart. Check the data range and use row 1 for headers. Google’s chart editing instructions document these controls.

Do not rely on the initial series allocation. In Customize → Series, select each named series and check Type and Axis:

• Packed boxes: Column, left axis.
• Inspection pass rate: Line, right axis.

The combo reference supports changing each series independently. If the editor offers a secondary-axis column/line preset, still inspect the resulting assignments. An automatically chosen arrangement is not an accuracy check.

Set and explain the scales

Use Customize → Chart & axis title to label the chart Synthetic packing and inspection results, the horizontal axis Period, the left axis Packed boxes (count) and the right axis Inspection pass rate (%). Keep the legend visible and distinguish the line from the columns without relying only on colour.

Under the vertical-axis controls, use a left minimum of 0 and maximum of 200 for this fixture. For the right axis use 0 to 1, displayed as percentages, so its endpoints represent 0% and 100%. Google’s axis guide documents bounds, label formatting and the right-axis control. Confirm the actual displayed endpoints before accepting the chart; do not type 100 as the upper bound for fractional percentage values.

The zero baseline preserves column-length comparisons. The full percentage domain is a deliberate teaching choice, not a universal chart rule. A narrower rate scale can highlight small changes, but it must be disclosed and never used to imply that a small change is a huge one.

Two axes do not make unlike units interchangeable. A crossing between the line and a column has no numeric meaning. Nor do four invented weeks demonstrate that packing more boxes causes a different pass rate. For readers likely to confuse the scales, two aligned charts with a shared period axis are a safer alternative.

Change one rate and restore it

Change C3, Week 2’s rate, from 95% to 75%. Its packed count stays 120. Expected passing inspections for that week become 30, the combined passing count becomes 86, and the weighted rate becomes 86%. Only the rate line’s Week 2 value should change in this chart.

Restore C3 to 95%. Recheck the four rate values, the count total 460 and the combined rate 94%. Then save and reopen in your own session and confirm the series types, axes, bounds and labels persist. This persistence check remains a reader task, not a result observed for this guide.

Troubleshooting

• The line hugs zero: inspect which axis the rate uses and whether cells contain fractions, percentages or text. Do not multiply the source values merely to make the line visible.
• An unexpected third series appears: check that the range ends at C5, not D5. Inspection denominators belong to the control calculation here.
• Rates appear as 90 rather than 90%: inspect the underlying value and axis number format separately.
• Counts appear as a line: select the count series specifically before changing its type; a setting for another series will not fix it.
• A point vanishes after changing the data: check fixed bounds and the source range before replacing a valid number. A future count above 200 needs a revised count-axis maximum.

For the general chart workflow, see create and edit a chart. For numeric X-coordinate spacing rather than categorical weeks, use the separate scatter-chart guide. This lesson owns the mixed-series and dual-unit checks, not those broader workflows.