How to Compare Two Graphs in Excel

Comparing sets of data is one of the fastest ways to uncover insights, and a well-designed chart can tell a story that raw numbers can't. When you place two graphs side-by-side or combine them into one, you immediately start to see relationships, trends, and outliers. This guide will walk you through several effective methods for comparing two (or more) graphs in Excel, from simple overlays to powerful combination charts.

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Why Bother Comparing Graphs in Excel?

Before jumping into the "how," it's helpful to understand the "why." Plopping data onto a chart is easy, but comparing charts is where real analysis begins. It helps you:

• Identify Relationships and Correlations: Does an increase in marketing spend lead to a rise in sales? Plotting both on the same timeline makes the correlation instantly visible.
• Track Performance Against Goals: You can plot your actual revenue against your projected revenue goal month-by-month to see how you're tracking.
• Spot Anomalies: Comparing this year's sales to last year's might reveal a sudden, unexpected drop in a specific month, prompting you to investigate further.
• Tell a More Compelling Story: Presenting a report that shows both website traffic and conversion rates gives a more complete picture than showing either metric in isolation.

In short, comparison turns data from a list of numbers into a useful decision-making tool.

Method 1: Create a Combination Chart with a Secondary Axis

The combination chart is your best friend when you need to compare two data sets that are measured on different scales. A classic example is plotting Revenue (in tens of thousands of dollars) against Conversion Rate (a small percentage). If you put them on the same axis, the conversion rate line would look like a flat line at the bottom, rendering it useless.

The solution is a combination chart that uses a secondary axis - giving each data set its own Y-axis to scale against.

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When to Use a Combination Chart:

• When you're comparing two different types of data (e.g., dollars and percentages).
• When one data set has values that are significantly larger than the other (e.g., # of site visitors vs. # of sales).
• When you want to show the relationship between two different metrics over the same period (e.g., time series).

Step-by-Step Guide:

Let's use an example of comparing monthly website sessions with the e-commerce conversion rate.

1. Organize Your Data

First, lay out your data in a clean, tabular format. Have your shared category (in this case, the month) in the first column, followed by your two data series in the next columns.

2. Insert the Combo Chart

Highlight your entire data range, including the headers (A1:C7 in our example). Go to the Insert tab on the Ribbon, click on the Combination Chart icon, and select a starter option. The "Clustered Column - Line on Secondary Axis" is often a perfect choice.

3. Configure the Chart Axes

Excel will instantly generate a chart. Now it's time to fine-tune it. Right-click on the chart and choose Change Chart Type…. This opens a dialog box that gives you full control.

In this window, you’ll see your two data series ("Sessions" and "Conversion Rate"). For each one, you can choose a chart type (like Column, Line, or Area). A column for Sessions and a Line for Conversion Rate work well visually.

The most important step is here: for the data series with the different scale (Conversion Rate), check the Secondary Axis box. You'll see the preview update immediately.

4. Tidy Up and Add Labels

Your chart is functional but needs some final touches to be clear and professional.

• Chart Title: Give it a descriptive title, like "Website Sessions vs. Conversion Rate."
• Axis Labels: Click the "+" icon next to the chart and check "Axis Titles." Label the primary vertical axis (the left one) as "Sessions" and the secondary vertical axis (the right one) as "Conversion Rate (%)" so everyone knows what they're looking at.
• Legend: Ensure the legend is clear so it's easy to differentiate the columns from the line. Adjust colors as needed via the "Format Data Series" menu.

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Method 2: Overlaying Both Charts on a Single Graph

If your data sets use the same unit of measurement (e.g., both are dollars or both are percentages), overlaying them on the same chart axis is a quick and effective way to demonstrate their relative change over time.

Imagine you want to compare sales of two products, "Product A" and "Product B," month-by-month over the same period. Overlaying their sales on a single x-axis in a chart allows you to see where each product is outperforming the other.

When to Use an Overlay Chart:

• When you are comparing "like-for-like" data (e.g., sales for Product A vs. Product B over the same time period).
• When both data series are measured in the same units (e.g., USD).
• When the range is narrow enough that the data can be comparatively visible without misleading visual comparisons.

Step-by-Step Guide:

1. Organize Your Data

As before, set up your data in columns. For the example of comparing sales of Product A vs. Product B, it should look like this.

2. Create the Initial Chart

Highlight the data for one series only (e.g., highlighting the "Product A" column, for A2:C9 in this case). If you include the headers, Excel will use them as the x-axis.

Go to the Insert tab and choose a Line type. A simple line will appear representing Product A sales.

3. Add the Second Data Series

Here's where the magic happens: Right-click in the white space of your chart and choose Select Data….

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Best Practices for Visual Comparisons

Comparing graphs isn't just about technical execution, it's also about presenting information clearly and honestly. Here are some tips to keep in mind:

• Use Consistent Axes: If you are not using a secondary axis, the y-axis on each of your compared charts should start at the same point (usually zero) and have the same maximum value, if possible. This prevents a small change in one graph from appearing more dramatic than a larger shift in another.
• Use Color Logically: Assign colors that make sense and are easy to differentiate. If comparing Product A and Product B, make your brand colors for each. Avoid overcomplicating unless you are illustrating growth and losses.
• Label Everything Clearly: Each chart should stand on its own without needing explanation. Use a clear title like "Year-on-Year Sales Growth," label the axes, and make sure the legend is readable.
• Cut the Clutter: The task is to get the reader to the data. Remove unnecessary gridlines, borders, or 3D effects that distract from the message. Your aim is to show the pattern in the data, letting your graphing skill shine.

Final Thoughts

Whether you're combining data on different scales into one complex chart, overlaying similar series on the same axes, or arranging a grid of small multiples for a dashboard view, Excel gives you the tools to do comparisons that reveal key trends and insights. These techniques transform a static spreadsheet into a dynamic, visual storytelling tool.

As powerful as Excel is, manually organizing data with the right chart type and formatting it perfectly still takes time and precision, especially when you're working with data from multiple sources like Google Analytics. Check out Graphed to see the unified view of comparison charts using natural language-through menus. You might enjoy something like "Compare website sessions versus conversion rate for the last six months as a combo chart," and we'll build a high-quality chart for you in seconds.