How to Make a Combo Chart in Looker with AI

Creating a chart that displays two different types of data, like website traffic numbers alongside your ad budget in dollars, can feel tricky. A combo chart is the perfect solution for this, and this tutorial will walk you through exactly how to build one step-by-step in Looker Studio (formerly Google Data Studio). We'll cover everything from structuring your data to styling your chart for maximum clarity.

What is a Combo Chart, and Why Should You Use One?

A combination chart, or combo chart, is a single visualization that combines two different chart types - most commonly, a bar chart and a line chart. Its main job is to help you display and compare two different metrics that are measured on different scales.

Imagine you're running a marketing campaign. You want to see how your ad spend (measured in thousands of dollars) is affecting your website's conversion rate (measured as a single-digit percentage). If you put both on a standard chart with one vertical axis, the conversion rate line would be completely flattened at the bottom, rendered useless by the scale of the ad spend bars.

This is where the combo chart shines. It uses two vertical axes, one on the left and one on the right. This lets you plot one metric against the left axis and the second metric against the right axis, allowing each to have its own appropriate scale while sharing a single horizontal axis (like time).

Common Use Cases for a Combo Chart:

• Sales Analysis: Comparing total revenue (bars, in dollars) with the number of units sold (line, in a raw count).

• Marketing Campaign Performance: Visualizing ad spend (bars, in dollars) against click-through rate or conversion rate (line, in percentage).

• Website Analytics: Tracking the number of new users (bars, as a count) against the bounce rate (line, as a percentage).

• Operational Efficiency: Comparing production volume (bars) with the cost per unit (line).

By pairing these metrics visually, you can spot correlations and trends almost instantly. You can easily see, "When we spent more on ads during the second week of March, did our website sessions actually increase?"

Getting Your Data Ready for Looker Studio

Before you jump into Looker Studio, the most important step happens outside the tool: preparing your data. A well-structured data source makes building any chart, especially a combo chart, significantly easier. The principle of "garbage in, garbage out" is especially true here.

For a standard combo chart, your dataset needs at least two things:

1. One Dimension: This is a category you want to measure things by. It’s what will go on your horizontal (X) axis. For time-based analysis, this is usually Date, Week, or Month. It could also be a categorical dimension like Campaign Name, Product Category, or Country.

2. Two Metrics: These are the quantitative numbers you want to measure and compare. For our combo chart, you'll need two, ideally with different units or scales. For example, Ad Spend (a currency) and Clicks (a whole number).

Here’s what your data might look like in a Google Sheet:

With data structured like this, you have everything ready. 'Date' is your dimension, while 'Ad Spend' and 'Website Sessions' are your two metrics.

Step-by-Step Guide: Building a Combo Chart in Looker Studio

Once your data source is ready (whether it’s in Google Sheets, Google Analytics, BigQuery, or another platform), it's time to build the chart inside Looker Studio. Let's create one that shows Ad Spend as bars and Website Sessions as a line.

Step 1: Create a Report and Add Your Data

Start by opening a blank Looker Studio report. If you haven’t already, you’ll be prompted to connect a data source. Find your source from the list of connectors (e.g., Google Analytics, Google Sheets) and add it to the report.

Step 2: Insert a Combo Chart

From the top menu, navigate to Insert > Combo chart. You’ll see a few options. The most common is the one showing bars and a line. Click to add it to your report canvas. Looker Studio will populate it with default dimensions and metrics from your data source, which we'll now change.

Step 3: Configure the 'Setup' Panel

With the new chart selected, look to the right-hand panel. This is where you tell the chart what data to display.

• Data source: Double-check that the correct data source is selected.

• Dimension: Drag your primary dimension into this field. In our running example, you would drag the Date field here.

• Metrics: This is the key part for a combo chart. You'll add both of your metrics here.

  • Drag your first metric, Ad Spend, into the metrics section. By default, it will be represented by bars.

  • Now, drag your second metric, Website Sessions, into the metrics section, right below the first one. This will form the line.

At this point, you'll have a chart, but it will probably look strange. The Website Sessions line might be floating awkwardly above the Ad Spend bars, or vice versa, because they're both sharing the same left-side Y-axis. The next step solves this problem completely.

Step 4: Style the Chart and Activate the Dual Axis

Switch from the 'Setup' tab to the 'Style' tab in the right-hand panel. This is where you'll unleash the true power of the combo chart by assigning different axes.

1. Scroll down until you find the "Series #1" and "Series #2" sections. In this case, Series #1 corresponds to our first metric (Ad Spend), and Series #2 corresponds to our second metric (Website Sessions).

2. Under Series #1 (Ad Spend), you can set the color and type (it should default to Bars). Make sure the Axis is set to Left.

3. Under Series #2 (Website Sessions), change the chart type from Bars to Line. Then, this is the most critical setting, find the Axis dropdown and change it from Left to Right.

Instantly, your chart transforms. An axis for Website Sessions will appear on the right side of the chart, perfectly scaled for that metric. The Ad Spend values will remain tied to the left axis. Now, both datasets are visually represented accurately and are easy to compare.

From here, you can continue to customize the look. You can add titles to each axis to avoid confusion (highly recommended!), change colors, add data labels, adjust grid lines, and more. Your goal is to make the chart as clear and easy-to-read as possible.

Using AI-Assisted Features in Looker Studio

The "AI" in creating charts sits more in the background of Looker Studio, assisting with calculations and, more recently, experimental features.

Using a 'Generated Chart' From a Prompt

Google is experimenting with generative features. In some accounts, you'll see a button to "Generate chart using a prompt." This is an early feature built on Google's Gemini models that allows you to describe the chart you want.

You could try typing a prompt like:

“combo chart showing daily Ad Spend and Website Sessions over time”

If the AI understands your data structure and intent, it can create a starting point for your combo chart, potentially saving you a few clicks in the 'Setup' panel. It’s still a new feature, so you'll likely need to fine-tune the settings manually in the 'Style' panel, especially for setting up the dual axes.

Intelligence Through Calculated Fields

A more common way to bring "intelligence" into your chart is by creating new metrics with calculated fields. Instead of just showing raw Ad Spend and Sessions, what if you wanted to see the relationship between Ad Spend and your Cost per Session?

You can create a new 'Cost Per Session' metric right inside Looker:

1. In the 'Setup' panel, click Add metric > Create field.

2. Give your new metric a name, like "Cost Per Session."

3. Enter the formula: SUM(Ad Spend) / SUM(Website Sessions)

4. Set the data type to Currency.

Now, you can use this newly created metric in your combo chart, perhaps comparing 'Cost Per Session' (line chart on right axis) with marketing-driven 'Revenue' (bar chart on left axis) to see if a rising cost per session correlates with higher overall revenue.

Best Practices for Readable Combo Charts

Building the chart is one thing, making it effective is another. Follow these tips to ensure your chart communicates its message clearly.

• Don’t Overclutter: A combo chart works best with two metrics. Adding a third (you can add up to five series in Looker) usually creates a "spaghetti chart" that’s confusing and difficult to interpret. Simplicity wins.

• Clearly Label Your Axes: Since there are two Y-axes representing different things, you must label them. In the 'Style' panel, under 'Left Y-axis' and 'Right Y-axis,' add clear titles like "Total Ad Spend ($)" and "Number of Website Sessions."

• Use Contrasting Colors: Make your bar and line series visually distinct. Avoid using similar shades of the same color. For example, a dark blue bar with a bright orange line is very clear.

• Provide Descriptive Titles: Give your chart a title that tells the viewer exactly what they’re looking at. "Campaign Performance: Spend vs. Sessions - Q2" is much better than "Combo Chart 1."

Final Thoughts

Ultimately, a combo chart is about telling a story by showing the relationship between two different metrics. By combining bars and lines with dual axes in Looker Studio, you can uncover insights that would be hidden if you looked at each metric in isolation and create powerful, informative dashboards for your team.

Of course, manually building reports chart by chart can still take time digging through menus and setup panels. That’s a large part of what we designed Graphed to solve. We integrated an AI data analyst that allows you to skip the manual setup and describe the dashboard you want in plain English. Instead of clicking through menus, I can simply type, "Show me a combo chart of Shopify revenue as bars and new customers as a line for the last 6 months," and it builds a live dashboard in seconds, with everything already connected and properly configured.