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Last Updated: January 10, 2022

Today I am going to show you how to use the new scroll depth trigger in Google Tag Manager to track how far website visitors scroll contents on your website.

Introduction to Scroll Depth

The term which denotes how far website visitors scroll contents on your website is called the ‘Scroll Depth’. 

This scroll depth can be vertical or horizontal, depending upon the type of scrolling available on your website. So we can have two types of scroll depths: Vertical Scroll Depths and Horizontal Scroll Depths

• Vertical Scroll depth measures how far website visitors scroll content on your website from top to bottom of a web page.
• Horizontal Scroll depth measures how far website visitors scroll contents on your website from left to right of a web page.

How is Scroll Depth Measured?

The scroll depth (whether it is vertical or horizontal) is measured in either percentage or pixels.

• If the value of the vertical scroll depth is 10% then it means 10% of the page was scrolled from top to bottom by a user.
• If the value of the vertical scroll depth is 50% then it means 50% of the page was scrolled from top to bottom by a user.
• If the value of the vertical scroll depth is 90% then it means 90% of the page was scrolled from top to bottom by a user.

90% Scroll depth can be considered equivalent to reaching the bottom of a web page as website visitors usually do not scroll 100% of a web page (unless the entire page fits in a default viewport)

// A viewport is the visible part of a web page.

Introduction to Scroll Depth Tracking

The tracking method which is used to measure ‘Scroll Depth’ is called ‘Scroll Depth Tracking’ or ‘Scroll Tracking’.

You can track scroll depth both vertically and horizontally depending upon the type of scrolling available on your website.

So we can have two types of scroll trackings:

Vertical Scroll Tracking and Horizontal Scroll Tracking

If vertical or horizontal scrollbars appear on most of your web pages and/or you run a content-rich website then you are a good candidate for implementing scroll tracking.

Through Scroll Tracking you can get an idea of how website visitors are consuming content on your website. For example, If you write very long articles but the majority of users exit your website after scrolling only 25% of your article pages then something is wrong with your website traffic or content.

You are either getting the wrong type of traffic on your website or your contents are not relevant to your target audience.

This is the kind of insight you can get through scroll tracking.

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Setting up Scroll Depth Tracking via Scroll Depth Trigger in GTM

Follow the steps below:

Step-1: Login to your Google Tag Manager (GTM) account and then click on the ‘Folders’ tab:

Step-2: Click on the ‘New Folder’ button.

Step-3: Name your new folder ‘Scroll Tracking’ and then click on the ‘create’ button. We are going to use this folder to store all tags and triggers related to scroll tracking.

Step-4: Click on the ‘Variables’ tab:

Step-5: Click on the ‘Configure’ button:

Step-6: Scroll down and then select the following three built-in variables related to Scroll tracking:

1. Scroll Depth Threshold
2. Scroll Depth Units
3. Scroll Direction

Step-7: Click on the ‘Triggers’ tab:

Step-8: Click on the ‘New’ button to create a new trigger.

Step-9: Name your new trigger as ‘Scroll Depth Trigger’ and move the trigger to the folder named ‘Scroll Tracking’ (by clicking on the folder icon next to the trigger name):

Step-10: Choose ‘Scroll Depth’ as trigger type:

Your screen should now look like the one below:

Step-11: At this point, you need to decide your scroll tracking setup:

• Whether you want to measure vertical scroll depth or horizontal scroll depth or both.
• Whether you want to measure scroll depth in percentage or in pixels.
• When the scroll depth event should fire.
• What pages the scroll depth trigger should fire.

You can either decide your own scroll tracking setup or you can use the one I use:

Here, I am measuring the vertical scroll depth in percentages.

The scroll depth event (gtm.scrollDepth) will fire whenever the vertical scroll depth of a web page crosses:

1. 10%
2. 25%
3. 50%
4. 75%
5. 90%

The scroll depth trigger will fire on all pages of a website.

Step-12: Click on the ‘Save’ button to complete the creation of the new trigger.

Step-13: Click on the ‘Tags’ tab:

Step-14: Click on the ‘New’ button to create a new tag.

Step-15: Name the new tag ‘Send Scroll Tracking data to GA’ and then move it to the ‘Scroll Tracking’ folder.

Step-16: Set up the new tag with following configuration:

We are going to use this tag to send the scroll tracking data to Google Analytics.

Step-17: Set the firing trigger of the ‘Send Scroll Tracking data to GA’ tag to ‘Scroll Depth Trigger’, we created earlier:

Step-18: Click on the ‘Save’ button to complete the tag set up.

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Step-19: Click on the ‘Preview’ button (on the top right-hand side) to preview and test your new scroll tracking setup:

Step-20: Navigate to a web page on your website where you want to test your new scroll tracking setup. You should see a ‘preview’ window at the bottom of your browser window:

Step-21: Now gradually scroll down your web page.

As you start scrolling down, you should see new ‘gtm.ScrollDepth’ event(s) being listed….one after the other….under the ‘Summary’ column:

Step-22: Click on one of the ‘gtm.scrollDepth’ events and then click on the ‘Data Layer’ tab:

Step-23: Now look at the values of following data layer variables:

• gtm.scrollThreshold
• gtm.scrollUnits
• gtm.scrollDirection

‘gtm.scrollDepth‘ is the name of the event that activates the Scroll Depth trigger.

‘gtm.scrollThreshold‘ is the datalayer variable which stores the value of the scroll threshold that was crossed.

So if you scrolled to 50% of the page then the value of this data layer would be ’50’.

Similarly, if you scrolled to 90% of the page then the value of this data layer would be ’90’.

‘gtm.scrollUnits‘ datalayer variable measure scroll depth in ‘percent’ or ‘pixel’. So the value of this data layer variable could be either ‘percent’ or ‘pixels’

‘gtm.scrollDirection‘ denotes the type of scrolling action which caused the scrolling threshold to be passed. Its value can be either ‘vertical’ or ‘horizontal’

If you see the values of the data layer variables then it means, scroll tracking is working correctly.

Step-24: Navigate back to your GTM account and then click on the ‘Leave Preview mode’ button:

Step-25: Click on the ‘submit’ button (on the top right hand side):

Step-26: Enter your version name and then click on the ‘Publish’ button.

Step-27: Navigate back to your website and scroll down a couple of web pages.

Step-29: Wait for 10-15 minutes and then navigate to ‘Behavior’ > ‘Events’ > ‘Top Events’ report in your Google Analytics view:

Step-30: Find and click on ‘Scroll Tracking’ event category:

In this event category you can find all of your scroll tracking data:

There are three more methods that you can use to install scroll tracking via Google Tag Manager.

You can read about these methods from this article: Implementing Scroll Tracking via Google Tag Manager

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