What is a combo chart?
A combo chart overlays two different chart types on a single canvas — typically bars and a line. For example, "Revenue (bars)" with "Year-over-year change (line)" lets you show quantity and ratio simultaneously. It's a staple of monthly business reports.
Use bars for totals and absolute counts; lines for ratios and indices. Pick the form that matches what each value is.
When to use it
Tips for making one well
1. Bars for absolute amounts, lines for ratios and trends
This is the basic rule. Countable amounts (revenue, visits) belong on bars; percentages and indices (growth rate, yield) belong on lines. The visual feels natural that way.
2. Use the second (right) Y-axis to separate units
If the bar's scale (e.g., 0–$2M) and the line's scale (e.g., 0–10%) differ widely, enable the second axis. On a single axis, one of them gets crushed.
3. Limit yourself to three or four series
Two bar series + one line, or one bar + two lines — about three to four series total is the readable limit. Beyond that, split the chart or focus on the series that matter.
4. Keep the line in front
This tool automatically draws lines in front of bars. The reader's eye flows naturally: "quantity (bars) → trend (line)."