How to Add a Horizontal Line in Google Sheets Graph

Adding a horizontal line to a Google Sheets chart is a simple way to add powerful context. Whether you're tracking performance against a goal, showing an average, or highlighting a benchmark, a simple line can instantly tell a story that raw data points alone can't. This guide will walk you through the cleanest and most effective method for adding reference lines to your charts, plus a few extra tips to make your reports even more insightful.

Why Bother Adding a Horizontal Line?

Before we jump into the "how," let's quickly cover the "why." A horizontal line acts as a visual anchor, giving your audience an immediate reference point. Here are the most common reasons you'd want to add one:

• Target/Goal Line: The most popular use case. If your sales team has a monthly target of $50,000, plotting that line against your actual sales chart immediately shows which months were above or below goal.
• Average Line: Want to see how daily website traffic compares to the monthly average? An average line instantly highlights days of unusual performance, both high and low.
• Threshold Line: This is useful for setting benchmarks or limits. For example, you might add a line for a minimum acceptable customer satisfaction score or a maximum allowable ad spend.
• Control Limits: In statistical process control (SPC), these lines (Upper and Lower Control Limits) help you identify if a process is stable or if there are variations that need investigation.

No matter your goal, the method is forgiving and flexible. Let's build one.

The Best Way: Using a Combo Chart

The most straightforward and reliable way to add a flat, horizontal line is by adding a new data series to your sheet and using the "Combo chart" feature. This tells Google Sheets to display one set of data as columns (or a line) and your new series as a separate, straight line.

Step 1: Set Up Your Data with a Reference Column

First, you need to prepare your data. Let’s say you have a simple table tracking monthly sales. To add a target line at $25,000, you just need to create a new column and fill it with that target value.

Here’s the setup:

1. Start with your primary data. For this example, we'll use Column A for the months and Column B for the corresponding sales figures.
2. Create a new column next to your data. Let's call it "Sales Target" in Column C.
3. In every row of this new column that corresponds to a month, enter your target value. It’s crucial that the value is identical in every cell. This is what creates the flat, horizontal line.

Your data should look something like this:

Step 2: Insert the Initial Chart

Now that your data is ready, let's create the chart.

1. Select all your data, including the new 'Sales Target' column and all the headers (from A1 to C7 in our example).
2. Go to the menu bar and click Insert > Chart.
3. Google Sheets will automatically analyze your data and suggest a chart type. Most likely, it will create a chart that shows both 'Sales' and 'Sales Target' as columns, which isn't what we want yet.

Step 3: Switch to a Combo Chart

This is where the magic happens. We'll tell Google Sheets to treat our two data series differently.

1. Double-click on your chart to open the Chart editor sidebar on the right.
2. If you aren't already there, click on the Setup tab.
3. Click the Chart type dropdown menu.
4. Scroll down until you find and select Combo chart.

Instantly, your chart will transform. Your original 'Sales' data will likely remain as columns, and the 'Sales Target' data will now appear as a nice, straight horizontal line across the chart. Google Sheets is usually smart enough to figure this out, but you can customize it further if needed.

Step 4: Customize Your Horizontal Line for Clarity

Your line is there, but you can make it stand out and look more professional. The default blue line might not contrast well or convey the right meaning.

1. In the Chart editor, click the Customize tab.
2. Expand the Series dropdown section.
3. In the "Apply to a series" dropdown, select your 'Sales Target' series. This ensures any changes you make will only affect the line, not your columns.
4. From here, you have several options to improve visibility:

After adjusting, your chart is clearer and communicates a much stronger message at a glance.

The Trendline Method: A Clever Workaround

While the Combo Chart method is the best all-around solution, there’s another way to achieve this using trendlines. This can be useful in specific situations or if you prefer a different approach.

The idea is to plot two hidden points on the chart that have the same Y-value (your target level) and then draw a trendline between them.

Step 1: Add a "Dummy" Data Series

For your trendline, you need at least two points. We'll add two new columns to your sheet, let's call them 'Dummy X' and 'Dummy Y'.

• For 'Dummy Y', enter your target value (e.g., 25000) into two cells.
• For 'Dummy X', you'll want to specify the start and end points of your line. If your main x-axis is categorical (like months), use 0.5 for the start and the total number of categories + 0.5 for the end (e.g., 6.5 for our 6-month chart). This positions the line nicely across the full plotting area.

Step 2: Add The New Series and Trendline

1. In the Chart editor, under the Setup tab, click 'Add series' and select the 'Dummy Y' data range.
2. You’ll see two dots appear on your chart at the target level.
3. Now, go to the Customize > Series tab.
4. Select your 'Dummy Y' series from the dropdown.
5. Scroll down and check the Trendline box. A straight line will instantly connect your two dots.
6. To finish, make the original dots invisible. Set the Point size to ‘None’ and the Line thickness to ‘0px’. All that’s left is your perfect horizontal trendline!

Troubleshooting Common Issues

My horizontal line is diagonal!

This is the most common problem and has a simple fix. It means the values in your special line column are not identical. Go back to your data sheet and make sure every cell in your 'Sales Target' column (or whatever you named it) contains the exact same number.

How do I add two horizontal lines? (e.g., a minimum and a maximum target)

Easy! Just repeat the process. Add another column to your sheet (e.g., 'Maximum Target'), fill it with your second reference value, and Google Sheets' Combo chart will automatically add it as another line. You can then customize each line independently under the 'Customize > Series' panel.

How do I hide the reference line from the legend?

If you don’t want 'Sales Target' appearing in your chart's legend, you can hide it.

1. In the Chart editor, go to Customize > Legend.
2. Click on the legend item text you want to hide (e.g., 'Sales Target'). Double-clicking should work.
3. Change the text font color to 'White' (or whatever your chart background color is). It won't be deleted, just made invisible.

Final Thoughts

Adding a reference line is a small tweak that delivers a huge improvement in clarity, transforming a simple data visualization into a powerful performance-tracking tool. While it's not a default button in Google Sheets, using the combo chart method is a reliable and flexible way to add targets, averages, or thresholds to any chart in just a minute or two.

We know that even simple reporting tasks like this can add up, especially when you’re pulling data from tools like Google Analytics, Shopify, or your CRM. At Graphed , we automate the entire process for you. Instead of manually setting up charts and reference lines in spreadsheets, you can just ask a question like, "Show me last month's revenue from Shopify versus our $30k goal," and our AI will instantly build a live dashboard. It saves teams hours every week, freeing them up to analyze insights instead of just preparing them.