A Guide to Custom Dimensions in Google Analytics 4

Updated: April 1st, 2025

Google Analytics (or any other similar tool) won’t help you much if you use it just “out of the box”. I’m talking about the classic “just add one line of JavaScript to your site and start tracking”. If you want to benefit from a platform, you have to customize your data collection.

Every business is unique, and you might want to track different things to understand how different parts perform.

One of the ways you can customize it is through custom dimensions. Instead of just having some generic data, you can go deep with your setup. Even though Google Analytics 4 offers better automatic tracking capabilities (compared to Universal Analytics), that’s not enough.

In this blog post, I’ll show you how to configure Custom Dimensions in Google Analytics 4 (with Google Tag Manager).

Table of contents

– Here’s what you will learn in this article –

• How to read this guide?
• PART I: Let’s start with some theory about dimensions
  • 1.1. What is a dimension?
  • 1.2. Custom Dimensions in GA4
    • 1.2.1. Scope
    • 1.2.2. Scope in Google Analytics 4
• PART II: The setup of custom dimensions + reports
  • 2.1. The process of creating Custom Dimensions in GA4
  • 2.2. How to Configure a Custom Dimension in GA4
  • 2.3. Register custom dimensions
  • 2.4. Where can I find custom dimensions in GA4 reports?
  • 2.5. User-scoped custom dimensions
  • 2.6. Item-scoped custom dimensions
• Final words

Video tutorial

If you prefer video content, here’s a tutorial from my YouTube channel.

How to read this guide?

I have split this blog post into two major parts:

• An introduction to custom dimensions
• An example of how to configure custom dimensions in Google Analytics 4 with Google Tag Manager

If you want to skip to the practical part, feel free to do so. But if you find something confusing, then read the first part as well.

PART I: Let’s start with some theory about dimensions

In this part, I’ll briefly explain the dimensions and their scope in Google Analytics.

1.1. What is a dimension?

Let’s start with the basics (because some readers of this blog post might be new to the game). What is a dimension?

Simply put, it’s a parameter/attribute or characteristic of data. It might be an attribute of a product, event, user, website, etc. It helps us better describe and understand what is happening, where it is happening, when it is happening, etc.

If this does not sound clear, here are some examples:

• A transaction occurs on a website. Its dimensions can be (but are not limited to):
  • Transaction ID
  • Coupon code
  • Latest traffic source, etc.
• A user logs in to a website, and we send the event login to Google Analytics. That event’s custom dimensions might be:
  • Login method
  • User ID, etc.
• A product is purchased. Its dimensions can be:
  • Product name
  • Product category
  • Product variant
  • Product size, etc.
• A logged-in user opens his/her account. Dimensions of a user can be:
  • User ID
  • Registration country
  • Pricing plan, etc.

To sum up, dimension is a parameter that describes something. What about custom dimensions?

Custom dimension is any attribute you additionally configure in your analytics tool because the default functionality does not cover that. And that’s where we move to Google Analytics.

1.2. Custom dimensions in Google Analytics 4

Even though there are many dimensions in Google Analytics, they cannot cover all the possible situations. Thus, custom dimensions are needed. Things like Page URL are universal and apply to many cases, but what if your business sells online courses (like I do)?

In Google Analytics, you will not find any dimensions related specifically to online courses. Why? Because probably 99.9%+ of businesses using GA have nothing to do with courses. And that’s why anything related specifically to online courses should be configured manually.

Enter Custom Dimensions.

1.2.1. Scope

A scope defines how a dimension or metric is applied within the data. Both built-in and custom dimensions in GA4 have scopes (we will take a closer look at them soon).

In the previous version of Google Analytics, there were four scopes:

• User
• Session
• Hit (event)
• Product

User-scoped custom dimensions are applied to all the hits of a user (hit is an event, pageview, etc.). For example, if you send a User registration country as a custom dimension, it will be applied to all the hits of that particular session AND to all the future hits sent by that user (as long as the GA cookie stays the same).

Session-scoped dimensions are applied to all hits of a particular session. For example, you could send the session ID custom dimension, and even if you send it with the last event of the session, all the previous events (of the same session) will get the value. This is done in the backend of Google Analytics.

Hit-scoped (also known as event-scoped) dimension applies only to that particular event/hit (with which the dimension was sent). For example, you could send an event “trial started” to Universal Analytics (GA3), and together with it, you could include an additional parameter, “pricing plan”. That dimension will be applied only to the “trial started” event.

Product-scoped custom dimension applies only to a particular product (that is tracked with Enhanced Ecommerce functionality). Even if you send multiple products with the same transaction, each product might have different values in their product-scoped custom dimensions, e.g., “product size”, “product color”, etc.

Why am I telling you this? Because some things have changed in Google Analytics 4.

1.2.2. Scope in Google Analytics 4

While session scope is still available in GA4, it applies only to some built-in dimensions (such as Landing page or Session default channel group). Session scope is not available for custom dimensions (at least not yet).

If you want to apply a dimension to all the events of a particular session, you must send that dimension with every event (that can be done on the code level (gtag) or in GTM). And the implementation depends on where you have that data in the first place. It can be in a cookie, data layer, or somewhere else.

So, right now, GA4 supports three scopes for custom dimensions:

• User-scope (applies to all subsequent events of the user after the user-scoped custom dimension is set))
• Event scope (applies to an event)
• Item scope (applies to a product if you have implemented ecommerce tracking)

Speaking of user-scoped custom dimensions in GA4, it’s important to note that if a custom dimension is set in the middle of the user session, it will apply only from that particular moment going forward. Past events of the same “session” will not be modified.

PART II: The setup of custom dimensions + reports

Now, let’s move to the 2nd part of this blog post, where I will show you how to configure custom dimensions and where to find them in Google Analytics 4 reports.

2.1. The process of creating Custom Dimensions in Google Analytics 4

First, let me start with a general overview of the process, and then we’ll look at an example.

Google Analytics 4 is pretty flexible when sending custom data to GA. If you use it to mainly stream data to BigQuery and then do the analysis there, you can send any custom parameters you want, and they will be visible in BigQuery.

You can just send the event name, say, “joined_waiting_list”, and then include the parameter “course_name”. And that’s it. However, if you want to use that parameter in the GA4 interface (and you will most likely do), you must register that custom dimension in the GA4 interface. In that case, you will need to:

• Register a parameter as a custom definition
• Start sending custom parameters with the events you want

The order DOES NOT matter here. But you should do that pretty much at the same time. If you start sending the parameter to Google Analytics 4 and only register it as a custom dimension, say, one week later, your reports will be missing that one week of data (because the registration of a custom dimension is not retroactive). However, raw data (e.g., streamed to BigQuery) will properly contain that parameter.

So, you might wonder, “What is the registration of a custom dimension?”. Let’s take a look at the example.

2.2. How to Configure a Custom Dimension in Google Analytics 4

Important: First, we will start with event-scoped custom dimensions because those are the most popular.

If you are new to event tracking in Google Analytics 4, you might also want to take a look at this guide (+ video).

In this example, I’ll be tracking menu link clicks. Every time a visitor clicks on a menu item, I will send an event and two additional parameters (that I will later register as custom dimensions), menu_item_url, and menu_item_name.

Note: Menu link click tracking trigger conditions differ on most websites (because of different click classes, IDs, etc.). Try to do your best to apply this example.

On a demo website, I have several menu links that I want to track.

First, I must create a trigger with the correct conditions that distinguish any click from a menu link click. Enable Google Tag Manager’s Preview mode and try clicking any of the menu links on a website. Once you click the first link, you should see the Link Click event on the Preview mode’s left sidebar.

If you don’t see it, you should:

• have at least one Just Links GTM trigger activated on a page
• or have “File download” or “Outbound links” tracking enabled in your Enhanced Measurement Settings within GA4

Let’s say that you don’t use Enhanced Measurement in GA4. Go to Google Tag Manager > Triggers > New > Just Links. Keep the trigger set to “All link clicks” and save the trigger.

By creating this trigger, we will enable the link-tracking functionality in Google Tag Manager.

Then go to Variables > Configure (in the “Built-in Variables” section) and enable all Click-related variables.

Refresh the preview mode (by clicking the Preview button once again).

Then, go to your website and click any of the menu links. Actually, click at least two of them. Return to the preview mode, and you should start seeing Link Click events in the preview mode. Click the first Link, Click event and go to the Variables tab of the preview mode.

Then click on the second Link Click event. I am currently looking for some variables that I could use to distinguish a menu link click. I don’t want to fire my GA4 event tag on any link click. I want to fire it precisely on a menu link click.

After taking a closer look, I see that both links contain the same Click Classes value, site-nav__link site-nav__link–main. By the way, nav means “navigation” in this context. Great! I will use this in my Just Links trigger.

Go back to the list of triggers in your GTM container and click the previously created trigger for All Link Clicks. We’ll edit it and add a condition: Click Classes contains site-nav__link–main

Save the trigger. Now, it’s time to create a Google Analytics 4 event tag. But before that, I will show you one good practice that will help you in the future.

Let’s create a constant variable that contains our Measurement ID. Go to Variables > Variable Configuration > Constant and paste your Measurement ID.

Save the variable. Then, go to Tags > New > Google Analytics > Google Analytics: GA4 Event.

Insert your newly created constant variable, and you should see a green checkmark. If you don’t see it, then cut and paste the constant variable name in that field (to trigger the validation).

Then, enter the event name. Its value is up to you. Any of the following options are perfectly fine:

• menu_click
• menu
• menu_item_click
• menu click
• etc.

These are just some examples. Since we are working with a custom event, we can name it whatever we want (as long as we follow the limitations of name length, for example).

In my case, I used the menu_link_click event name. But this time, sending just the event name is not very useful. You’d probably want to know which exact menu items are clicked more often. How about we also send the name of the menu item and the URL?

We could do that by sending additional event parameters. Even though you could use parameters that are already mentioned in the documentation of the Enhanced Measurement (like link_url and link_text), let’s create two custom parameters (because I just want to show you how to configure them).

I am going to pass two parameters, menu_item_url, and menu_item_name. I made these parameter names up, and you can do it too. That’s what the flexibility of the data model offers.

To send custom parameters, you must expand the Event Parameters section in the Google Analytics 4 event tag and then click Add Row.

Enter the name of the first parameter. In my case, that is menu_item_url. In the Value field, I will insert a variable that returns a clicked URL. Luckily, GTM already offers such a variable. It’s called Click URL. Click the Insert Variable button and then select the {{Click URL}} variable.

Let’s add another parameter, menu_item_name. For that purpose, GTM offers another built-in variable, {{Click Text}}. Insert it as well. Since visitors of your website can translate your page, {{Click Text}} value will also change, hence you will see a more diverse list of collected values in your GA4 reports.

If you want to send more parameters, you can do that. You can send up to 25 parameters with a single event. These two parameters will eventually become custom dimensions in Google Analytics 4.

Assign the previously created Just Links trigger to this tag. Save the tag. Refresh the GTM Preview mode and click a couple of your menu items. Go back to the Preview mode and click those Link Click events. Check if the GA4 event tags for Menu Link Clicks have fired.

Now, you will need to go to Google Analytics 4 and check DebugView. You will learn more about that in this chapter of the blog post. If the debug view is not working properly, read this article.

And now, the time has come to register those parameters as custom dimensions.

2.3. Register custom dimensions

If you want to see/use them in things like Funnel exploration, Free Form, see their reporting cards in standard reports, etc., you must register custom parameters in the GA interface.

In Google Analytics 4, go to Admin > Custom Definitions. Since we sent two custom parameters with the menu link click, we must register them here.

Click the Create Custom Dimensions button and then enter:

• The name of the parameter. You can enter whatever you want. This is just how the dimension will be displayed in your reports. You can name it “menu_item_url”, “Menu item URL”, or anything else.
• Scope. Since we want to apply this parameter only to one event (and not to all events of the same user), we need to select Event
• Event parameter. This is where you have to enter its name precisely as you entered it in the GTM tag. If your parameter name is menu_item_url, you must enter it here exactly like that. Don’t worry if the autocomplete feature of that field does not show your parameter yet. Just enter it and save the dimension.

Then, register a second parameter (in my case, that was menu_item_name) and save it. By the way, I sometimes use the words “custom parameter” and “custom dimension” interchangeably. In general, custom metrics and custom dimensions are both grouped as custom parameters.

And now we wait. Within the next 24 hours, the custom parameters will start appearing in your Google Analytics 4 reports.

2.4. Where can I find custom dimensions in Google Analytics 4 reports?

This blog post focuses mainly on creating custom dimensions in Google Analytics 4. I will not dive deep into how to find insights, raise questions, answer questions, etc. You can learn all of that in this course.

However, I can show you several places where you can find the dimensions you have just sent to Google Analytics 4.

Here are some of the reports:

• Admin > Events (this will show just the list of events with counts. Nothing fancy.
• Reports > Engagement > Events. Keep in mind that the sidebar of the “Reports” section is highly customizable, thus in your location, the location of this report might differ.
• Explore (a.k.a. Exploration reports)

But that is not all. Since GA4 is an event-based analytics platform, every report is affected by events that you send (in one way or another). The reports mentioned above are just the most notable examples.

2.4.1. “Reports → Engagement → Events” report

This is an overview of all events that were sent to your property + a couple of charts. Below them, you will see a list of events, and if you click on any of them, you will take a closer look at that event’s data.

Note: The GA4 sidebar is highly customizable. The location of the “Events” report in your property might differ, so keep looking.

2.4.2. Explore (a.k.a. Exploration reports)

This is where you will be able to drill down into your data. In the Explorations, you can use reports such as Free Form, Funnel Exploration, Path Exploration, etc.

Here is an example of a Free Form report. Remember that you will need to wait up to 48 hours for the data to come into your reports. So, if you don’t see the data now, be patient.

Let’s say I want to see how visitors with different device categories interact with the menu bar of my site. Remember, I set up the menu_click event?

So, let’s go to Explore and click on the Free Form block.

Then in the Variables column, I need to include the menu_item_url custom dimension because I want to see how many clicks did get each menu URL. Click the Plus icon and then find the menu_item_url dimension. Select it, and it will be included in the list of possible dimensions in the report.

If you CANNOT see the menu_item_url (or whatever custom parameter you are looking for), you must register that custom parameter in Admin > Custom Definitions. Then, wait for 24 hours until the data appears in the reports. If the reports don’t work properly, wait for even longer.

Then let’s edit the Tab settings. Remove the existing dimensions in the ROWS and include the custom definition that you want to include. In my case, that’s menu_item_url.

In the COLUMNS section, I used the Device category dimension. In the VALUES section, select the metric that you wish to see. I used the Event Count.

Then, you will need to filter only to those events that actually contained the menu_item_url dimension. In my case, that is just a menu_click event. That’s why at the bottom of the Tab Settings section, you should enter a filter: Event name exactly matches  menu_click.

That’s it. Your report will now display how different device categories are clicking menu items, which ones are the most popular, and how many times they were clicked.

Also, don’t forget to change the date range if needed. You can do that in the top-left corner of the Exploration interface.

You can also use event data in funnel reports, but let’s keep it for another tutorial (hopefully) in the future.

2.5. User-scoped custom dimensions

In GA4, user-scoped custom dimensions are set to all the events from that particular moment onwards. Past events of the same session will not be modified.

Also, if you want to send the user-scoped custom dimensions with GTM, there are several available places/options. Here are some examples.

Also, if you want to watch about this, here it is:

#2.5.1. “User properties” section of the event tags

When setting user-scoped custom dimensions, they are called “User properties” on the GTM tag level. You can individually set them in each event tag by going to the “User properties” section.

But this is not very convenient because if you have 100 GA4 event tags, you might need to do this same update 100 times (once per each tag). That’s why I want to recommend a more convenient option.

#2.5.2. Event settings variable

In Google Analytics 4, you can create an Event settings variable, set user properties inside of it, and then reuse that same variable across multiple tags.

In Google Tag Manager, go to Variables > New > Variable Configuration > Google Tag: Event Settings.

In that variable, click Google Analytics User Properties and then insert the parameter you want to use in GA4 as a user-scoped custom dimension. Also, give this the settings variable a name and save it.

Then, you will need to update all your Google Analytics tags (this applies to GA4 event tag and Google Tag).

In the Google Tag, go to Shared event settings, and then in the Event Settings Variable, select the variable you just created. Save the tag.

Then, edit all your GA4 event tags one by one. Go to Event parameters, and in the Event Settings Variable field, insert that new variable.

But you still need to manually update all your tags – you might say. Yes, but only once. If you decide to add/edit/remove user properties in your tags in the future, you will just need to go to the Variables section of GTM, find that settings variable, and then edit it once. This change will then be inherited by all GA4 tags that use it.

When you send the user properties to Google Analytics 4, you must register them as user-scoped custom dimensions in the GA4 interface.  To do that, you must go to Admin > Custom Definitions > Custom Dimensions and click Create Custom Dimensions.

Then enter the following settings:

Make sure the scope is User.

As always, you must wait up to 24 hours for the data to appear in reports.

2.6. Item-scoped custom dimensions

They allow you to send custom data about each product on your website (because the list of predefined item dimensions in GA4 is limited). For example, you can send:

• Item size
• Item weight
• Item availability (“in stock” or “out of stock”), etc.

This feature can give you an amazing opportunity to analyze the data from more angles, tailored to business needs.

There are several rules you need to follow:

• The custom dimensions work only if they are used inside the items array (this array is reserved specifically to GA4 ecommerce tracking).
• If you are using Google Tag Manager to control GA4 data flow, item parameters must be stored in the data layer or in some custom variable that outputs the entire items array. For example (size is the custom parameter here):

  dataLayer.push({
    event: "view_item_list",
    ecommerce: {
      items: [
       {
        item_id: "SKU_12345",
        item_name: "Stan and Friends Tee",
        size : "XL", // I added this custom parameter
        price: 9.99,
        quantity: 1
      }
  ]
  });

• Item-scoped dimensions will not work if you configure them as regular event parameters, for example:
  
  If you send a parameter as displayed in the screenshot above, it will be treated as an event-scoped parameter.

Once your item data is properly stored in the data layer, you can enable this checkbox in your GA4 event tag and it will be sent to GA4.

If you have installed GA4 with Google Tag (GTAG) directly in the source code of the website, then take a look at the documentation. But the principle here is very similar. Your item-scoped custom parameters must be inside the items array (in each product).

Custom Dimensions in Google Analytics 4: Final Words

With the rise of Google Analytics 4, custom dimensions have become the fundamental functionality needed even for beginners. If you want to track an event and include any additional text parameter, you’re dealing with custom dimensions.

The process is pretty straightforward here. You must send some custom data to GA4 and register a parameter as a custom dimension (if you want to use/see that parameter in regular Google Analytics 4 reports).

However, if you are using Google Analytics 4 to stream data to BigQuery and analyze it there, then there is no need to register dimensions. Even unregistered parameters will be available in BigQuery.

Do you have some questions about custom dimensions in Google Analytics? Feel free to post a comment below.