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Last Updated: January 7, 2022

In this article, I am going to talk about sending the Google Analytics Client ID via GTM (Google Tag Manager).

Understanding Client ID in Google Analytics

Google Analytics identifies a user as unique through a combination of a unique random number and the first timestamp (i.e. the time of the first visit). This combination is called the Client ID.

Client ID is created and assigned by the Google Analytics _ga cookie.

The _ga cookie is made up of the following four fields:

The first field is the version number like GA1.

The second field is the number of components at the domain separated by a dot.

By default, the _ga cookie is set on the top-level domain with the root level (/) path. So if you have set a cookie at the top-level domain like optimizesmart.com then the second field would have a value of 2 as there are 2 components separated by a dot. One component is ‘optimizesmart’ and the second component is ‘com’.

If you have set up a cookie at the sub-domain level, like analytics.optimizesmart.com, then the second field would have a value of 3 as there are now three components separated by a dot. The first component is ‘analytics’. The second component is ‘optimizesmart’. The third component is ‘com’

The third field is a random unique ID (randomly generated number). Here 1368576646 is the random unique id.

The fourth field is the first timestamp i.e. the time when the cookie was first set for the user. Here 1596648643 is the first timestamp.

The third and fourth fields together make the client ID. So, the client ID would be 1368576646.1596648643 

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How to find Client ID (aka _ga cookie in browser)

To view your Google Analytics cookie (Client ID) for a specific site in the Chrome browser, open the site and follow the below steps

Step-1: Click on three dots at the left corner of your Chrome browser and then click on ‘Settings’.

Step-2: Scroll down and click on ‘Cookies and other site data’ under ‘Privacy and security’.

Step-3: Scroll down and click on ‘See all cookies and site data’.

Step-4: Look for your website domain and click on it.

Step-5: Click on ‘_ga’ and in the content, you will find your client ID.

A Google Analytics cookie can exist only on the device and browser where it has been set up. Since client ID is stored in a GA cookie, the client ID can exist only on the device and browser where it has been set up. Because of this, Google Analytics cannot identify unique users across different web browsers and devices, by default.

In GA reports, Client ID is available as a primary dimension only in the User Explorer report:

The User Explorer report, shows website usage data (sessions, average session duration, bounce rate, revenue, etc) for each user, via the Client ID dimension:

Since Client ID dimension is available only in the User Explorer report, you cannot use this dimension in any other GA report. That makes analyzing website usage data at the user level quite difficult.

The only solution to this problem is to collect client id data through your efforts and send it to GA as a custom dimension.

Since Client ID is completely anonymous, it cannot be used to personally identify a person (unless you choose to combine it with personally identifiable data).

Sending Client ID to GA as a custom dimension via GTM

Follow the steps below to send Client ID to GA as a custom dimension via GTM/

Step-1: Navigate to your GA property and click on ‘Admin’.

Step-2: Click on ‘Custom Definitions’ under ‘Property’.

Step-3: Click on ‘Custom Dimensions’.

Step-4: Click on ‘+New Custom Dimension’.

Step-5: Give your custom dimension a name like ‘Client ID’. Then click on the ‘Scope’ drop-down.

Step-6: Select the scope as ‘User’.

Step-7: Click on ‘Create’.

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Step-8: Note down the index number of your custom dimension:

We will use this index number later while setting up a custom dimension in GTM.

Follow the below steps to configure GTM.

Step-9: Navigate to your GTM account.

Step-10: Click on the ‘Variables’ link in the left-hand side navigation menu.

Step-11: Click on ‘New’ under ‘Use-Defined Variables’.

Step-12: A new window will pop up like below. Give it a proper name and click on ‘Variable configuration’.

Step-13: In ‘Variable configuration’ you will see several types of user-defined variables as below. Click on ‘Custom JavaScript’.

This variable is a custom JavaScript function which is used to pass website parameters within variables.

Step-14: Paste the following code into the code window.

function(){

try {

   var tracker =

ga.getAll()[0];

   return

tracker.get(‘clientId’);

 } catch(e) {

   return false;

 }

}

This variable returns client ID if there is no error. Otherwise, it returns false.

The ‘try’ JavaScript statement is used to test a block of code for errors. The ‘catch’ JavaScript statement is used to handle the error.

Now let’s create a new event tag that fires on the window load event. We are going to use this tag to send client ID as a custom dimension to GA:

Step-15: Click on ‘Tags’ and then click on ‘New’.

Step-16: Give your tag a descriptive name and click on ‘Tag configuration’.

Step-17: An overlay will appear on the right-hand side with a list of tag templates. Select ‘Google Analytics: Universal Analytics’.

Step-18: Click on the drop-down under ‘Track type’ and select ‘Event’.

Step-19: Now In the event category type ‘Client ID’.

Step-20: Now click on the ‘+’ icon under ‘Event action’ and select the JavaScript variable that we created earlier (Return Client ID).

Step-21: Now similar to the earlier step, click on the ‘+’ icon under ‘Event value’ and select the ‘Page path’ variable.

Step-22: Set ‘Non-Interaction Hit’ to ‘True’ and your tag will look like below:

Step-23: Now select the Google Analytics setting variable. Here {{GA Default Settings}} is a Google Analytics settings variable that I use. It returns the property ID.

Then mark the checkbox ‘Enable overriding settings in this tag’ and click on ‘More settings’ and then on ‘Custom Dimensions’.

Step-24: Now click on ‘+Add custom Dimension’.

Step-25: Now in the input box under ‘Index’, type the index number we noted earlier. And then click on the ‘+’ icon under ‘Dimension value’ and select the JavaScript variable that we created earlier (Return Client ID).

Now let’s create a trigger for this event.

Step-26: Click on ‘Triggering’.

Step-27: Click on the ‘+’ icon.

Step-28: Give your trigger a proper name and click on ‘Trigger configuration’.

Step-29: An overlay will appear on the right-hand side. Select ‘Window Loaded’.

Step-30: Select the radio button ‘Some Window Loaded Event’.

Step-31: Click on the drop-down ‘Click Classes’ and select ‘Return Client ID’ variable.

Step-32: Select operator ‘does not equal to’ and value ‘false’.

Now you may ask, why am I not using the ‘Container Loaded’ event to send the custom dimension?

This is because the ‘Return Client ID’ JavaScript variable does not seem to resolve on the ‘Container loaded event’.

And then check for Window Load  in Summary tab It seems to resolve on window load event:

To send Client ID as a custom dimension via the pageview tag, I would have to fire the GA pageview tag on the window load event and this is something, I don’t want to do.

If I fire the GA pageview tag on the window load event then it will delay the firing of the tag and can create tracking issues in the case that some event fires before the pageview. So, to avoid this problem, I am sending client ID as a custom dimension via event tag.

I do not want this event tag to impact bounce rate that is why I have set the event as a non-interaction event:

Now let’s save this tag.

Step-33: Click on ‘Save’ to save the trigger.

Step-34: You will be redirected to ‘Tag Configuration’. Again click on ‘Save’ to save the tag.

Congratulations! You have successfully configured Google Analytics and GTM for Client ID.

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Debugging and Validation

Step-1: Click on ‘Preview’ in GTM.

Step-2: Now In the input box under URL, type your website URL and click on ‘Start’.

Step-3: A new tab will open with your website URL. Switch back to the debugger tab and click on the window loaded in the ‘Summary’ tab.

As you can see from the above image, our event tag is firing on window load.

Click on the event to check more details.

Google Analytics reports with Client ID

You can now use the client ID as a primary dimension in GA custom reports.

You can now use the client ID as a secondary dimension in GA standard reports:

You can also see client ID data in the ‘Top Events’ report under Behavior > Events:

Frequently Asked Questions About Sending Google Analytics Client ID via GTM (Google Tag Manager)