GA4 Event Parameters: What They Are and How to Use Them

Everything here comes from Google's own pages, mainly the Analytics Help article Event parameters, the Analytics event parameters table, the event collection limits and the developer guide Set up event parameters, plus the other pages linked where they are used. Checked on 12 November 2026. Turning a custom parameter into a report dimension is covered in our custom dimensions guide; this page stays with the parameters themselves.

What an event parameter is

Google's Help Center defines it as an additional piece of data about a user interaction on a website and/or app. An event says what happened (a click, a search, a lead); its parameters say which link, which term, how much it was worth.

Parameters are key-value pairs. Google's example is the recommended level_end event:

gtag("event", "level_end", {
    level_name: "The journey begins...",
    success: true
  });

Here level_name and success are the parameters. They are not the same thing as dimensions and metrics. In Google's words, event parameters let you collect data, while dimensions and metrics let you analyze the data. Parameter data feeds dimensions and metrics, and those are what you see in reports, explorations and audiences.

Four places parameters come from

Google's About events page sorts events into four types, and each brings its own parameters:

• Automatically collected events, such as page_view and session_start, come with parameters you don't have to code.
• Enhanced measurement events, such as scroll and file_download, also carry their own parameters when the option is on.
• Recommended events have predefined names and parameters that Google publishes; you send them yourself.
• Custom events carry whatever parameters you define.

The difference that matters is reporting. The developer guide says the parameters on automatically collected and enhanced measurement events, and the required and optional parameters of recommended events, populate prebuilt dimensions and metrics. Other parameters need a custom dimension or metric before you can report on them.

Parameters sent with every event

The automatically collected events page lists several parameters that GA4 collects by default with every event, including custom ones. On a web stream they are these, with the dimension each one fills according to Google's parameter table:

App streams get app_version, firebase_screen_id and firebase_screen_class instead. Many automatic events add their own parameters on top; the same page lists them event by event, and notes that these names help when you work with raw data in BigQuery.

You can override page_location, for example on a single-page app, but Google warns that if you assign an invalid URL path, the Page location dimension will be empty.

Enhanced measurement parameters

Each enhanced measurement event carries its own parameters. A few that people look for most:

The scroll event fires the first time a visitor reaches 90% of the page, so percent_scrolled shows 90. Clicks also send link_domain, file downloads send file_name and link_url, and every video event has its video parameters. Most of these have a ready dimension, such as Search term, File extension and Link URL. The settings, and what each option really measures, are in our enhanced measurement guide.

Recommended event parameters

For recommended events, Google publishes the parameters to send with each one in its recommended events reference. The Help Center says these parameters unlock prebuilt dimensions and metrics that you can use in reports and audiences, and the recommended events page tells you to send them with their prescribed parameters. Some common ones:

• search: search_term, required.
• login and sign_up: method, optional, for example "Google".
• generate_lead: value and currency, plus an optional lead_source.

Google's example for a lead:

gtag("event", "generate_lead", {
  currency: "USD",
  value: 30.03,
  lead_source: "Trade show"
});

Value and currency go together: the reference says currency is required if you set value, and if you mark the event as a key event, it recommends setting a value. Ecommerce events also take an items array with item-level parameters; our GA4 ecommerce guide covers those.

Use the exact names. A parameter you call searchTerm instead of search_term is just a custom parameter to GA4 and will not fill the Search term dimension.

Adding your own parameters

You can add custom parameters to recommended events as well as custom ones. Google's example: on the search event, add a search_location parameter to record which search box on your site was used.

The developer guide gives two ways to send them:

• One event: add the parameter in that event's command, as in the examples above.
• Every event on the page: put it in the config command or use the set command. Parameters set with gtag('set') apply to all later gtag('event') calls on the page, so the set command has to run before the event fires.

In Google Tag Manager, open the GA4 event tag, expand Event Parameters, type a parameter name such as button_label and pick a variable for the value, for example Click Text or a data layer variable. Preview, then publish.

Sending is half the job. The developer guide is clear that without registration the parameter data is collected but isn't available for reporting. That step, and the limits on custom dimensions, are in our custom dimensions guide. If you want to rename or fix a parameter after the fact without touching the tag, see modifying and creating events.

Collection limits

From Google's event collection limits. GA4 does not log anything over these:

Two details are easy to miss. Characters are counted on the encoded URL length, and the limits are the same for English and for double-width languages such as Japanese. The custom item parameters come on top of the prescribed item parameters of each recommended ecommerce event. Upgrading to Analytics 360 raises some limits, but not the character limits.

There is also a size cap per hit: About events says Google Analytics has a 16 KB size limit on event data each time data is sent, and if a batch of events goes over it, the whole batch is not processed. Long parameter values on many events add up.

Parameter naming rules and reserved prefixes are listed in our custom dimensions guide and in Google's event naming rules.

Checking parameters in Realtime and DebugView

You can see parameters as soon as they arrive, before any custom dimension exists:

• Realtime: for the Event count by Event name card of the Realtime report, the About events page says you can click an event to see the event parameters that were sent with the event.
• DebugView: the DebugView report shows one device's events; click an event to see its parameters. The developer guide adds that its Parameters tab shows the merged list, including parameters set globally with set. Debug mode has to be on first.

How to turn on debug mode and read the stream is in our DebugView guide. In the standard reports, the Events report detail page shows parameters once they are registered; Google says it can take up to 48 hours after registering a custom dimension or metric before data shows.

Event parameters vs user properties

An event parameter describes one action. A user property describes the person, such as a plan type, and once set it applies to that user's later events. If a value belongs to the user rather than the click, use a user property. Setting user properties is covered in our custom dimensions guide, and logged-in IDs belong in User-ID, not in a parameter.

Our view

This is our opinion, not Google's guidance. Before adding a custom parameter, check whether a recommended event already has one for the job; the prebuilt dimension saves a custom dimension slot. Write down every parameter name, which events send it and whether it needs registering, and keep one style (lowercase with underscores). Check each new parameter in DebugView before you publish, then again in Realtime. Keep personal data such as names and email addresses out of parameter values entirely.

Frequently asked questions

What are event parameters in GA4?

Extra details sent with an event as key-value pairs, such as the page URL, the search term or the value of a lead. They collect the data; dimensions and metrics built from them are what you analyze in reports.

How many parameters can a GA4 event have?

Up to 25 event parameters per event. Parameter names can be up to 40 characters and values up to 100 characters, with longer limits for page_title, page_referrer and page_location.

Which parameters does GA4 collect automatically?

On web streams, every event carries language, page_location, page_referrer, page_title and screen_resolution, among others. Automatically collected and enhanced measurement events add their own, such as percent_scrolled on scroll or file_extension on file_download.

Do I need to register recommended event parameters?

No. The required and optional parameters of recommended events fill prebuilt dimensions and metrics. Only parameters you invent yourself need a custom dimension or metric.

Where can I see event parameters before registering them?

In the Realtime report, by clicking an event in the Event count by Event name card, and in DebugView, by clicking an event once debug mode is on.

Want your GA4 events and parameters planned and tagged properly? See our website development service and all our services, or email [email protected].