Add reference lines to charts

Reference lines show how the data in a chart compares to a reference value. For example, you can use reference lines to visualize daily sales against a target sales figure, or show the average revenue per store and compare each store to that average.

Reference line example: weekly sales vs. target.

Reference lines vs. trend lines

Reference lines let you show target values and set thresholds and benchmarks so you can see how your data matches expectations or goals.

Trend lines reveal the overall direction of the data in a chart. Trend lines can help you see patterns and make predictions from otherwise random-appearing data. In Looker Studio, you can add trend lines to time series and scatter charts.

Add a reference line

You can add reference lines to time series, line and combo charts, bar and column charts, area charts, and scatter charts.

1. Edit your report.
2. Select a chart. You can add reference lines to Cartesian type graphs (for example, time series, bar, area, and line charts).
3. On the right, in the properties panel, select the STYLE tab.
4. Click Add a reference line.
5. Select the reference line Type.
   You can base a reference line on a constant value, a metric, or a parameter.
6. Configure the reference line using the options below.

You can add up to 10 reference lines per chart.

Reference line options

Type

Determines the value upon which the reference line is based.

Constant value

Base the reference line on a value you type in. For example, if your sales target is $10,000 per day, enter 10000. For a percentage value, enter the number as a decimal (.5 equals 50%).

Metric

Base the reference line on a metric that appears in the chart.

Parameter

Base the reference line on a parameter. Only single-valued numeric parameters are allowed.

Calculation

For metric-based reference lines, choose the aggregation to apply to the selected metric. For example, if the chart is visualizing Users by Week, you can create a reference line showing the average number of weekly users by choosing the Users metric and Average calculation.

Available calculations:

• Average
• Median
• Percentile
  • Enter the percentile as a whole number between 0 and 100.
• Min
• Max
• Total

Axis

Display the reference line on the chart's X, Y, Left-Y, or Right-Y axis. This option applies to constant value and parameter-based reference lines. The available axes depend on the chart type.

Label

Display a custom label for the reference line.

If you leave this blank, Looker Studio supplies a default label. For constant value reference lines, the label is "Reference Line #n." For metric reference lines, the default label is the type of calculation applied. For parameter reference lines, the default label is the parameter name.

Line color, weight and style

Set the appearance of the reference line.

Reference line example showing a 90th percentile calculation on a reading test scores metric, with line color, weight, and style options applied.

View a reference line

Reference lines appear with either a default label, or a custom label you supply. Hover over the line to display a tooltip showing the reference value.

Remove a reference line

To remove a reference line from a chart:

1. Edit your report.
2. Select the chart.
3. On the right, in the properties panel, select the STYLE tab.
4. Locate the reference line you want to remove, then click .

Edit charts with reference lines

If you change the chart type, Looker Studio deletes any reference lines not supported by the new chart type.

If you remove a metric from the chart, Looker Studio deletes any reference lines associated with that metric.

Limits of reference lines

• Reference lines are only available for numeric axes. Reference lines on date axes aren't supported.
• Metric-based reference lines can only consider values currently displayed in the chart. For example, if you add a reference line to a bar chart with 10 bars, data from any additional bars aren't included in the calculation.
• You can't add a reference line to 100% stacked charts.
• Stacked column, stacked bar, and stacked area charts only support constant value and parameter reference lines.