GA4 key events: what they are and how to set them up

GA4 key events are the events you flag in Google Analytics 4 as the actions that matter most to your business, such as a purchase, a lead form submission or a click to call. They used to be called "conversions" in GA4; Google renamed them in 2024 so that the word "conversion" now refers to the actions Google Ads counts and bids on, which keeps the two systems from being confused.

The change sounds cosmetic, but it changes how you read reports, how you set up Google Ads bidding and how you explain numbers to a client or a manager who sees two different totals for the "same" action. This guide covers what GA4 key events are, how to mark one, how they differ from Google Ads conversions, how counting works, where they show up in reports and the setup mistakes that quietly break measurement.

What are GA4 key events?

Everything a user does in GA4 is recorded as an event: page_view, scroll, click, form_submit, purchase and so on. Most of those events are context. A key event is an ordinary event that you have told GA4 to treat as important. Once an event is marked, GA4 counts it in the key events metric, calculates key event rates and uses it in attribution reporting.

Nothing about the event itself changes when you mark it. The same generate_lead event fires in the same way with the same parameters. What changes is how GA4 summarises it. That is why the rename matters: a key event is a reporting decision inside Analytics, while a conversion is now a measurement object inside Google Ads that can drive automated bidding.

Why Google renamed conversions to key events

Before the rename, GA4 and Google Ads both used the word "conversion" for different things. GA4 counted a conversion every time a marked event fired, using GA4's own attribution. Google Ads counted conversions against ad clicks, using its own counting rules and attribution model. Teams regularly compared the two and assumed one of them was broken. Splitting the names makes the distinction explicit: GA4 has key events, and the subset of key events you import into Google Ads (or measure with the Google Ads tag) become conversions there.

How to mark an event as a key event

There are two ways to do it, and both live in the Admin area of your GA4 property. Google's help asks for the Editor role or above to mark an existing event, and the Marketer role or above to create a new key event.

Option 1: mark an existing event

1. Open Admin and, under Data display, choose Events.
2. Find the event in the Recent events tab. Only events GA4 has already received will appear here.
3. Click the star icon next to the event. The star turns solid and the event is now a key event.

Option 2: create a new event as a key event

1. Open Admin and, under Data display, choose Events, then click Create event.
2. Type the exact event name, for example generate_lead. Event names are case sensitive, so Generate_Lead would be a different event.
3. Turn on the Mark as key event toggle and choose the counting method.
4. Click Create. GA4 will start counting the event as a key event as soon as it arrives.

The second option is useful when you are preparing a new site or a new form and want the key event ready before any traffic exists.

Making a narrower key event from a broad event

Marking works on the event name, not on a parameter. If your site sends one form_submit event for the newsletter box, the contact form and the quote request, marking form_submit turns all three into key events. To track only quote requests, go to Admin, then Events, then Create event, and build a new event (say quote_request) that fires when form_submit arrives with a matching parameter such as the form ID or the page location. Mark the new event as the key event and leave the broad one unmarked.

Key events are not retroactive

Marking an event applies from that moment forward. GA4 does not reprocess historical data, so last month's generate_lead events will not appear in the key events metric if you only mark the event today. Plan the marking before a campaign starts, and note the date in your measurement documentation so nobody misreads the jump in the trend line.

Which events are key events by default?

On web data streams, purchase is marked as a key event automatically. App properties come with their own defaults, such as first_open and in_app_purchase. If you enable Ads Personalization with a linked Google Ads account, GA4 also marks events such as add_to_cart, begin_checkout, view_item and session_start as key events, so review the list after linking. Everything else is your choice. Lead generation sites usually mark generate_lead or a custom form event. Sites that sell through chat or phone mark click events on the phone number or messaging link.

Counting method: once per event or once per session

Each key event has a counting method, which you can change in Admin under Data display, Events, on the Key events tab, through the More menu next to the event. A change only applies to future data.

• Once per event counts every occurrence. If a user submits two forms in one session, GA4 records two key events. This is the default for new key events and suits purchases, where each transaction matters.
• Once per session counts the key event at most once in a session, however many times the event fires. This suits leads, where a user who submits the same form twice is still one lead, and actions that can fire repeatedly by accident, such as a thank-you page reload.

A worked example with illustrative numbers: a session where a visitor clicks the call button three times produces three key events with "once per event" and one with "once per session". If you bid on calls, the second setting reflects real demand much better.

GA4 key events vs Google Ads conversions

The table below compares the two side by side, because most reporting disputes come from treating them as the same number.

Importing key events into Google Ads

Link the GA4 property to the Google Ads account first (Admin, then Product links, then Google Ads links). In Google Ads, go to Goals, then Conversions, add a new conversion action and choose the import option for Google Analytics 4. You will see the key events from the linked property. Once imported, review the conversion action's settings, such as counting, conversion window and attribution, because Google Ads uses them for reporting and bidding. Google notes that some of these settings may not be editable in Google Ads, in which case you change them in GA4.

Two settings deserve attention after import. The first is primary or secondary: only primary actions feed bidding strategies such as Maximize conversions or target CPA. The second is duplication. If the same lead is measured both by the Google Ads tag and by an imported GA4 key event, and both are primary, Smart Bidding sees every lead twice. Keep one as primary and set the other to secondary for observation.

Why the numbers never match exactly

Expect GA4 and Google Ads to disagree, even when both are set up correctly. Google Ads credits a conversion to the click date and only counts conversions it can tie to an ad interaction. GA4 credits the event date and includes every channel. Counting methods may differ between the two. Consent choices, ad blockers and cross-device journeys affect each tool differently. A gap is normal; a gap that suddenly widens is the signal to investigate.

Where key events show up in GA4 reports

• Acquisition reports. The traffic acquisition and user acquisition reports include a Key events column and a key event rate. The column header has a dropdown that lets you switch from "all key events" to a single one, which is the fastest way to see which channel produces quote requests rather than every key event combined.
• Engagement reports. The events reports show event counts, and key events can be filtered or compared there.
• Advertising section. Attribution and conversion path reports use key events to show which channels contribute before the final action.
• Explorations. Free-form and funnel explorations can use key events and the session key event rate or user key event rate metrics, which is where most deeper analysis happens.
• Realtime and DebugView. Use these while testing. DebugView, under Admin, shows events from a debug-enabled browser in sequence, so you can confirm a key event fires once, with the right parameters, before you rely on it.

Google allows up to 24 hours for a newly marked key event to show in standard reports, so do not judge a new key event by the first few hours of data.

Common GA4 key event mistakes

1. Marking engagement events as key events. Flagging page_view, session_start or scroll inflates the key events total until it means nothing. If every session "converts", the metric cannot tell you which campaign works.
2. Marking both steps of the same action. Marking form_start and form_submit, or begin_checkout and purchase, double counts one journey. Keep the final step as the key event and analyse the earlier steps in a funnel exploration.
3. Thank-you pages that fire twice. A page that can be reloaded or bookmarked will fire its event again. Switch to "once per session" for leads, or fire the event on the actual submit action instead of the page load.
4. Broad events marked whole. One form_submit for every form on the site mixes newsletter sign-ups with sales enquiries. Create specific events and mark those.
5. No value on purchase or lead events. Without the value and currency parameters, revenue reports stay empty and value-based bidding has nothing to work with.
6. Double importing into Google Ads. Two primary actions for one lead teach Smart Bidding to chase volume that is not there.
7. Forgetting that history is not rewritten. Comparing a period before marking with a period after marking shows a false jump.

What this means for Thai marketers

A large share of Thai enquiries never touch a web form. Visitors tap a LINE link, open Messenger or call the number on the page. If only form submissions are key events, those channels look like they produce nothing. Create specific events for clicks on LINE links, on tel: links and on messaging buttons, mark them as key events with "once per session", and import only the ones that represent real sales intent into Google Ads. Thai sites also run cookie consent banners because of the PDPA, so the share of visitors you can observe depends on consent; that reduces observed key events in both tools and is another reason the totals will not match.

If you are rebuilding measurement, a structured GA4 setup and migration review is the place to define key events once, document them and connect them to Google Ads campaign bidding. Lead-heavy businesses should align key events with their lead generation funnel, and online stores should check purchase values against their order system as part of any ecommerce marketing work.

FAQ about GA4 key events

Are GA4 key events the same as conversions?

No, GA4 key events are the renamed version of what GA4 used to call conversions, while "conversions" now means the actions Google Ads counts. A key event becomes a Google Ads conversion only when you import it into Google Ads or measure the same action with the Google Ads tag.

Does marking an event as a key event change past data?

No, marking an event only affects data collected after you mark it. Historical events stay as ordinary events and are not added to the key events metric for earlier dates.

Should I use once per event or once per session?

Use once per session for leads and once per event for purchases. Leads are usually one per person per visit, so repeated fires should not inflate the count, while each separate purchase is real revenue.

How many key events should a property have?

Keep the list short and limited to actions that represent business value, typically a handful. GA4 also caps the number: up to 30 key events on a standard property and 50 on Analytics 360, not counting the default ones. The real limit is clarity: if you cannot explain why each key event matters, it should probably be a normal event.

Why do GA4 key events and Google Ads conversions show different totals?

The two tools use different attribution, counting rules and dates. Google Ads credits ad interactions on the click date, while GA4 includes every channel on the event date, so a steady gap is expected and only a sudden change needs investigating.

Key events are only as useful as the decisions behind them. If your GA4 property has a long list of starred events and nobody is sure which ones feed bidding, it is worth an audit before the next budget review. Relevant Audience can help you clean up the setup through our GA4 service.