GA4 Event Tracking Series ⓪ —— Rules and Limits for GA4 Events

Updated: January 12, 2025

GA4 is event-driven, and all data in it is tracked through events, so there are various events

Event Structure

An event consists of an event name and event parameters.

• There is no limit on the number of event names for the Web
• The number of event names for the App is limited to 500, and automatically collected events and enhanced measurement events are not included in the limit.

Event Name

• Event name is at most 40 bytes
• Event names are case sensitive. For example, my_event and My_Event are distinct events.
• Event names can include English and non-English words and letters.
• Do not use reserved prefixes and event names.
• Event names must start with a letter. Use only letters, numbers, and underscores. Don’t use spaces.

Event Parameter

• Each event can set up to 25 Event Parameters
• Event Parameters can be divided into Default (built-in) Event Parameters and Custom Event Parameters.
  • Default Event Parameters: also called Built-in event parameters, are what all events have by default.
    • For Web, there are 5 default event parameters:
      • page_location（No more than 1000 characters）
      • language
      • page_referrer （No more than 420 characters）
      • page_title （No more than 300 characters）
      • screen_resolution
    • For APP, there are 3 default event parameters:
      • app_version
      • firebase_screen_id
      • firebase_screen_class
  • Custom Event Parameters: It is the user-defined event parameter, which can be divided into two types:
    • Event-scoped custom dimensions: which is a character-type event parameter, has a maximum of 40 characters and a limit of 50
    • Event-scoped custom metrics:  which is a numeric-type event parameter, has a maximum of 100 characters/length and a limit of 50
  • Event parameters need to be set in GA4 Custom Definitions before they can be used

Types of events

Events can be divided into four types:

• Automatically Collected Events：After deploying the basic GA4 tracking code or SDK, events will be automatically collected without any settings.
• Enhanced Measurement Events：Some built-in basic tracking events, just turn them on in the data flow to automatically track
• Recommended Events ：Events with predefined names and parameters by Google, the event names and parameters are fixed, you need to set up sending data to these events, and there will be data in the event report.
• Custom Events ：It is your custom event.

Principles of Event Tracking

If you want to do an event tracking, follow the order of automatic collection events——enhanced measurement events ——recommended events —— custom events to see which type of event is available. If there is, use that type of event. If not, use custom events.

Read More： 

• GA4 Event Tracking Series ⓪ —— Rules and Limits for GA4 Events
• GA4 Event Tracking Series ① —— Automatically Collected Events
• GA4 Event Tracking Series ② —— Enhanced Measurement Events
• GA4 Event Tracking Series ③ —— Recommended Events
• GA4 Event Tracking Series ④ —— Custom Events (gtag Method）
• GA4 Event Tracking Series ⑤ —— Custom Events (Attributes Method)
• GA4 Event Tracking Series ⑦ —— Custom Events (addEventListener Method）
• GA4 Event Tracking Series ⑧ —— Custom Events (jQuery Method)
• GA4 Event Tracking Series ⑨ —— Custom Events (ga-data Method)
• GA4 Event Tracking Series ⑩ —— Custom Events (dataLayer.push Method）
• GA4 Event Tracking Series ⑪ —— Create Event（Codeless Event Tracking）
• GA4 Event Tracking Series ⑫ —— Modify Event