Event Parameter
AnalyticsAlso: Event Properties · Event Metadata
Quick definition
An event parameter is a piece of extra information attached to a tracking event. When Google Analytics 4 (GA4) records a button click or page view, event parameters describe the context: which button, which page, which product, which value. The event says what happened. The parameter says the details.
How it varies across Australia
Most Australian businesses using GA4 collect event parameters automatically but register very few as custom dimensions, meaning the detail is captured in the raw data but never surfaces in reports. The gap between what is tracked and what is actually usable in analysis is wider than most teams realise.
See data and tracking scores across Australian industries →The three types of parameters you will encounter
Parameters GA4 adds to every event without any setup: page location, page title, session ID, language.
Parameters GA4 adds when enhanced measurement is on: scroll depth, outbound link URL, video title.
Parameters your team defines and sends with specific events: product category, form name, plan type.
What it actually means
Think of a tracking event like a photograph and an event parameter like the caption. GA4 records that a purchase event happened. The event parameters tell you the purchase value, the currency, the item category, the coupon code applied. Without them, you have a photo with no context.
Every event in GA4 can carry up to 25 parameters. Some come for free: GA4 automatically attaches page URL, page title and session information to almost everything. Others require deliberate configuration. A product view event with no parameters attached is near-useless for analysis. A product view event with item name, item category, item price and item list position attached lets you answer questions like which categories drive the most engaged browsing.
The catch is that collecting a parameter and being able to report on it are two different things. GA4 stores raw event parameters in the data stream, but to surface a custom parameter in Explorations or reports, it must first be registered as a custom dimension in the GA4 property settings. Many teams send rich parameter data that sits invisible in BigQuery exports while their GA4 reports show nothing useful.
Event parameters are closely related to how conversion events are defined. A purchase conversion event without a value parameter attached is a count with no revenue signal. Attribution models that use conversion value rely on that parameter being present and correct.
The event tells you someone clicked. The parameter tells you what they clicked, why it mattered, and what it was worth.
How it shows up
Event parameters show up in GA4 in three places. In the DebugView while you test your implementation, where every parameter value is visible in real time. In Explorations, where registered custom dimensions become filterable and breakdownable dimensions. And in the raw event export to BigQuery, where every parameter is stored in an event_params array regardless of whether it was registered.
If you are using Google Tag Manager (GTM), parameters are usually passed as dataLayer variables. The event fires, the dataLayer push includes the parameter values, and GTM maps those to GA4 event parameters in the tag configuration.
For server-side tracking implementations, parameters are defined in the Measurement Protocol payload or through a server-side GTM container before the hit reaches GA4.
The Australian context
Australian teams implementing GA4 for the first time often inherit an event structure designed around Universal Analytics (UA) goals and events, which had a completely different parameter model. The UA model used category, action and label fields. GA4 uses named parameters with no structural limit on what they describe. The migration is not one-to-one and the teams that try to map old UA fields directly to GA4 parameters usually end up with a data model that fits neither platform well.
Where people get this wrong
Related terms
Common questions
How many event parameters can I send in GA4?
GA4 allows up to 25 custom parameters per event. Automatically collected parameters do not count toward this limit. You can register up to 50 custom event-scoped dimensions and 25 user-scoped dimensions per property before hitting the registration limit.
Do I need to register every parameter as a custom dimension?
Only if you want to see it in GA4 reports and Explorations. Parameters you do not register are still collected and available in a BigQuery export if you have one connected. For most teams without a data analyst, unregistered parameters are effectively invisible.
What is the difference between an event parameter and a UTM parameter?
A UTM parameter is appended to a URL and tells GA4 where traffic came from. An event parameter is attached to a specific event that fires on the site and describes what happened during that visit. UTM parameters feed session and traffic source data. Event parameters feed behavioural and conversion data.
Why are my custom parameters not showing up in GA4 reports?
The most common reason is that the parameter has not been registered as a custom dimension in GA4 Admin under Custom Definitions. Registration is a separate step from sending the parameter. Also note that custom dimensions only show data from the point of registration forward, not historically.
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New Rebellion is a marketing intelligence consultancy. We build tools, score Australian businesses on how their marketing actually performs, and publish Debrief every day. This dictionary is part of how we work in the open.
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