Custom Dimensions in GA4: 6 Simple Steps to Create Them

Hi everyone! Today's lesson fixes one of the most common GA4 frustrations: data you know you are sending, but can never find in a report.

You added a parameter to an event, checked DebugView, and there it was. Then you opened your reports a day later and found nothing. The data was never lost. GA4 simply needs you to register it first, and that is exactly what custom dimensions in GA4 are for. Let's walk through it with real screenshots from a live property.

Every screenshot in this guide comes from a working GA4 property for a technical blog. You will see the same screens and the same buttons when you follow along.

We will cover the three scopes, the exact steps to create a dimension, the limits you need to plan around, and the mistakes that leave you staring at "(not set)".

Every GA4 event can carry extra details called parameters. A download event might carry a brochure name, and a signup event might carry a plan type.

GA4 collects those parameters, but most of them stay hidden from reports until you tell GA4 to treat them as a dimension. Custom dimensions in GA4 are that bridge between a raw parameter and a column you can actually report on.

Google's help article on custom dimensions and metrics explains that event scope dimensions report on custom event parameters, while user scope dimensions report on custom user properties.

Think of it this way. The parameter is the raw data you send. The custom dimension is the reporting label that makes it usable.

Custom dimensions versus custom metrics

The same Custom definitions page also creates custom metrics. The difference is simple: a dimension describes something, while a metric counts or measures it.

A brochure name is a dimension, because you group rows by it. A file size in kilobytes or a quoted order value is a metric, because you add it up or average it.

Most marketers start with custom dimensions in GA4 and only add metrics later, once they know which numbers they want to total in reports.

Scope decides what a value describes. Pick the wrong one and your reports will slice data in ways that make no sense.

Most dimensions belong in event scope. Relevant Audience's guide to scopes and quotas calls choosing the wrong scope the most common design mistake, and notes that scope cannot be changed after you save.

User scope values come from user properties. Once set, GA4 applies them to that visitor's later events too, which is why they suit stable traits rather than one off actions.

The whole process takes about two minutes once the parameter is already being sent. Here is the path, step by step.

1. Click Admin at the bottom left of GA4.
2. Under Data display, open Custom definitions.
3. Stay on the Custom dimensions tab and click Create custom dimension.
4. Enter a clear Dimension name and an optional description.
5. Choose the Scope, then pick or type the exact Event parameter name.
6. Click Save, then wait for new data to arrive.

Here is the Custom definitions page on our live property. Notice it already holds six dimensions that a WordPress plugin created automatically.

The Custom definitions page. The six rows here were added by Google Site Kit, a reminder to check what already exists before adding more.

Plugins like Site Kit quietly use part of your quota. Always review this list first, so you know how many slots you really have left.

Clicking Create custom dimension opens the form on the right. Here it is filled in for the link_url parameter that outbound clicks send.

The new custom dimension form, filled in for link_url. The parameter dropdown suggests names GA4 has already received.

Before you click Save, though, there is one check that saves quota. We actually closed this form without saving, and the next section shows why.

GA4 already ships with hundreds of predefined dimensions. Many common parameters, including link_url, are already available as built in dimensions in Explore, so registering them again just burns a slot.

You can see this inside an exploration. Searching for "link" in the dimension picker shows five predefined Link dimensions plus Outbound, with zero custom ones needed.

The Explore dimension picker. Link URL is predefined, so there is no need to register it as a custom dimension for explorations.

Use the planner below before you create anything. It checks the name, flags parameters GA4 already covers, warns about values that change too often, and shows how much quota you have left.

The planner flags high cardinality for a reason. Stackmatix's GA4 custom dimensions guide explains how dimensions with too many unique values push rows into an "(other)" bucket in your reports.

A dimension is only a label. Something on your website still has to send the parameter with each event.

Here is a real example. A brochure download event sends two custom parameters, and a user property marks the visitor as a distributor.

// Event parameters, register as Event scope
gtag('event', 'download_brochure', {
  brochure_name: 'Flow Meters 2026',
  product_line: 'flow'
});

// User property, register as User scope
gtag('set', 'user_properties', {
  customer_type: 'distributor'
});

Pick a naming convention and stick to it

Lowercase names with underscores, like product_line, match the style Google uses for its own parameters. They are also easier to read in DebugView and harder to mistype.

Write the convention down for your team before anyone adds new tracking. A shared list of approved custom dimensions in GA4, with the parameter name, scope and owner for each one, prevents duplicates and keeps your quota under control.

You would then create two event scope dimensions, one for brochure_name and one for product_line, plus one user scope dimension for customer_type.

If you use Tag Manager instead of gtag, the logic is the same. Our guide to custom event tracking with Google Tag Manager shows how to add parameters inside a GA4 event tag.

Keep collection limits in mind too. Relevant Audience lists a 40 character cap on parameter names, a 100 character cap on most values, and a maximum of 25 parameters per event.

Most problems with custom dimensions in GA4 come down to timing, naming or quota. Here are the ones we see most often.

Expecting old data to appear

Registration is not retroactive. Relevant Audience notes that Google says a new dimension becomes usable 24 to 48 hours after it is created, and that earlier events are not reprocessed.

Optimize Smart's guide to GA4 data delays adds that you may see "(not set)" for a new custom dimension during its first 24 hours. That is normal, not a broken setup.

Registering everything just in case

Fifty slots sound generous until a few plugins and old experiments take half of them. Register only what you will actually report on.

If you hit the limit, you can archive old dimensions. Measureschool's guide shows the archive prompt warning that it cannot be undone, and Relevant Audience adds that you must wait 48 hours before reusing freed slots.

Using values that are too unique

Session IDs, timestamps and full user agent strings make terrible dimensions. They create so many unique values that GA4 groups most of them into "(other)".

Mistyping the parameter name

A dimension pointing at a parameter that is never sent stays empty forever. Copy the name straight from DebugView rather than typing it from memory.

Sending personal information

Never pass email addresses, phone numbers or full names as parameters. Google Analytics policies do not allow personally identifiable information, and a single careless form field can put your whole property at risk.

Use an internal ID or a broad category instead. "Distributor" or "returning buyer" tells you everything you need for reporting, without exposing who the person actually is.

Once data flows in, custom dimensions in GA4 appear in three main places. Each one suits a different kind of question.

• Standard reports. Add the dimension as a secondary dimension, or customize a report so it shows by default.
• Explorations. Import it into the Variables panel and use it as a row, column or filter. Our GA4 free form exploration guide shows this step by step.
• Audiences. Build an audience such as every visitor whose customer type is distributor.
• Looker Studio. Registered dimensions appear in the GA4 connector, ready for dashboards.

Analytics Mania's custom dimensions guide walks through each of these report locations in more detail if you want to go deeper.

If your parameters come from the automatic events covered in our GA4 enhanced measurement guide, check the predefined list first. Many of them are already there.

Frequently Asked Questions