What is a Custom Dimension in Google Analytics?

Google Analytics is great at telling you what users did on your site - which pages they visited, how long they stayed, and where they came from. But it often falls short on telling you who those users are in ways that matter to your business. This is where Custom Dimensions come in, allowing you to add your own business-specific data to GA4. In this guide, we'll walk through what they are, why they’re indispensable for meaningful analysis, and how you can set them up to get richer insights into your audience.

What Are Custom Dimensions in Google Analytics 4?

Think of the standard data in Google Analytics as pre-labeled filing cabinets. You have cabinets for "City," "Device," and "Traffic Source," and GA automatically files every user's data into the right place. However, what if you need a cabinet for "Subscription Plan," "Author Name," or "Customer Type?" Google has no idea what that is for your business. That's what custom dimensions are for - they are the custom-labeled filing cabinets you create to organize users and their actions based on your unique business context.

In short, a custom dimension is a piece of extra information, an attribute, that you send to Google Analytics to describe a user, a session, or a specific event. This data isn't tracked by default, you need to define it and send it yourself.

Custom Dimensions vs. Standard Dimensions

Standard dimensions are the out-of-the-box attributes that GA provides for all users. Custom dimensions are the ones you create.

• Standard Dimension Examples: Browser, Country, Landing Page, Session source/medium.
• Custom Dimension Examples: User Login Status, Membership Tier, Blog Post Category, Form Submission Type.

Custom Dimensions vs. Custom Metrics

It’s easy to get these two mixed up, but the distinction is simple. Dimensions describe things, while metrics count things.

• Dimensions are attributes (text-based): They answer questions like "who," "what," and "where." The color of a car ("Red") is a dimension.
• Metrics are numbers (quantitative): They answer questions like "how many" or "how much." The number of red cars sold (15) is a metric.

For example, if you run a blog, the author's name is a dimension (e.g., 'Jane Doe'). The number of views her articles received is a metric (e.g., '12,500').

Understanding Scoping

In Google Analytics 4, custom dimensions have a "scope," which determines which events the dimension will be applied to. There are two primary scopes:

1. Event Scope: The dimension only applies to the specific event for which it was set. For example, if you want to track which blog post someone shared, you might create an event-scoped custom dimension called post_title that gets sent only with the "share" event. It tells you about that single action.
2. User Scope: The dimension applies to all future events for that user once it has been set. This is perfect for classifying your users. If a user logs in and you set a user-scoped custom dimension like membership_tier to "Premium," all of their subsequent actions (page views, clicks, purchases) will be tagged with that dimension until it changes.

There is also an "Item" scope specifically for e-commerce, which allows you to tag properties for individual products in an order, like item_color or item_size.

Why Bother Setting Up Custom Dimensions?

Setting up custom dimensions is an extra step, but the payoff is immense. It transforms your Google Analytics account from a generic web traffic tool into a powerful business intelligence platform tailored to your specific goals.

Gain Deeper Insights Into Your Audience

Standard GA reports can show you that users from mobile devices convert at a certain rate. That's useful, but a custom dimension can tell you how "Logged-in Premium Members" on mobile devices behave compared to "Guest Visitors" on mobile devices. Suddenly, you can segment your analysis to go far beyond demographics and understand how different user cohorts interact with your site.

Questions you can answer:

• Do paying customers view more pages than free trial users?
• What percentage of our traffic comes from logged-in users?
• Which subscription plan generates the most engagement with our content?

Track Business-Specific Data Points

Every business model is different. A SaaS company cares about plan tiers, an e-commerce store cares about member status, and a publisher cares about content categories and authors. Custom dimensions allow you to report on the concepts that truly drive your business.

Examples:

• Publisher Blog: Track author_name and post_category to see which authors and topics perform best.
• SaaS Company: Track account_type (Free, Pro, Enterprise) to analyze product usage by pricing tier.
• E-commerce Site: Track customer_ltv (categorized as Low, Medium, High) to see if high-value customers use the site differently.

Improve Your Marketing and Content Strategy

When you align your analytics with your business structure, you can make smarter decisions. If you discover that articles written by "Expert Contributor Jane" drive twice as many newsletter signups as other authors, you know who to ask for more content. If "Pro Plan" users are reading all your advanced tutorials, you know that content is highly valued by your best customers and should produce more of it.

How to Set Up a Custom Dimension in GA4: A Step-by-Step Guide

Setting up a custom dimension is a two-part process. First, you need to send the data to Google Analytics. Second, you need to tell Google Analytics how to interpret that data.

Step 1: Plan Your Custom Dimension

Don't just start setting things up. First, identify the question you're trying to answer.

Example:

• Question: "How does sitewide engagement differ between our free users and our premium subscribers?"
• Data Needed: We need to know the subscription status for each user.
• Custom Dimension Plan: We'll create a user-scoped dimension called "Subscription Plan." The identifying key (or parameter) will be subscription_plan, and the values can be "free" or "premium."

Step 2: Send the Data to GA4 (Usually with Google Tag Manager)

GA4 can only report on data it receives. You need to configure your website to send your custom data along with GA4 events. The most common and flexible way to do this is with Google Tag Manager (GTM).

While a full GTM tutorial is beyond this article's scope, the basic idea is:

1. Make the data available on your website. Your developers can push this information into a "Data Layer" when a user logs in. It might look something like this code snippet on login:

dataLayer.push({
  'event': 'login_success',
  'subscription_plan': 'premium' 
}),

1. Capture the data in GTM. You will create a "Data Layer Variable" in GTM that reads the value of subscription_plan.
2. Attach the data to your GA4 tags. In your GA4 Configuration tag or a specific event tag, you add an "event parameter" or "user property." For our example "Subscription Plan" dimension, which is user-scoped, you would add it as a "User Property."

Once GTM is set up and published, your website will begin sending this subscription_plan parameter to Google Analytics with every event for that user moving forward.

Step 3: Register the Custom Dimension in GA4

Just because GA4 is receiving your custom data doesn't mean it knows what to do with it yet. You need to officially register it so you can use it in your reports.

Steps:

1. Navigate to the Admin section in GA4 (the gear icon in the bottom-left).
2. In the Property column, click on Data display > Custom definitions.
3. Click the blue "Create custom dimensions" button.
4. A configuration panel will open. Fill out the fields carefully:

• Dimension name: This is the user-friendly name that will appear in your reports. Example: Subscription Plan
• Scope: Choose "User" or "Event" based on your plan from Step 1. Example: User
• Description: Add a brief description. Example: Tiers (Free/Premium)
• User Property: This must exactly match the parameter name you sent from your website/GTM. Be careful with spelling and case sensitivity. Example: subscription_plan

1. Click save.

It will take about 24-48 hours for your data to start populating this custom dimension in reports. You can then add it as a primary or secondary dimension in your Exploration reports or see it on cards in your standard reports by adding a comparison.

Real-World Examples of Custom Dimensions You Can Use Today

Need some inspiration? Here are a few practical examples categorized by business type that can deliver immediate value.

For SaaS & Membership Sites

• Dimension: subscription_tier (e.g., Free, Pro, Enterprise) - Analyze feature usage and engagement across different customer segments. Scope: User.
• Dimension: user_role (e.g., Admin, Editor, Viewer) - Understand how different job roles interact with your product. Scope: User.

For Content Publishers & Blogs

• Dimension: author_name - Track the performance of each author to identify your top contributors. Scope: Event (sent with each page_view).
• Dimension: post_category (e.g., Marketing, Sales, Finance) - Discover which content categories engage your audience the most. Scope: Event.

For E-commerce Stores

• Dimension: login_status (e.g., Logged In, Guest) - Compare shopping behavior and AOV between registered members and guest shoppers. Scope: Event or User.
• Dimension: customer_ltv (e.g., High, Medium, Low) - Create segments based on historical customer value to see how your best customers browse new offerings. Scope: User.

Final Thoughts

Custom dimensions allow you to step outside the standard limitations of Google Analytics and track the data that truly defines your unique business goals. By sending in attributes like user roles, content categories, or customer tier, you convert it from a mere traffic-reporting tool to an authentic source of business intelligence.

While powerful, setting this up correctly in GA4 and Google Tag Manager requires careful planning and can involve a bit of a learning curve. Yet the deeper insights this uncovers are more than worth the effort. It's often the single best way to get actionable, reliable answers to your company’s most important questions from your data. That's actually why we built Graphed. The AI will handle building reports for you based on all your custom and standard dimensions. With Graphed, there's no need to be an expert in the Exploration Reports section - you can simply ask, “Show me the number of sessions by 'Premium' vs. 'Free' users” and get an instant answer instead of digging through menus.