GA4 key events and conversions: the difference explained

A key event is an event you mark as important in GA4, such as a submitted quote form or a purchase. A conversion is what Google Ads measures and bids on ^[1]. Only mark actions that are worth money, only let them fire after a real submission, and choose one primary source per action in Google Ads.

GA4 now calls conversions key events ("belangrijke gebeurtenissen" in the Dutch-language interface); the word conversion is reserved for Google Ads ^[1]. Any event can become a key event if you mark it, and a key event only becomes a conversion once you pass it on to Google Ads. In GA4 you only see those conversions under Advertising, not in the standard reports ^[1].

A wrongly marked key event pollutes every report in GA4, and in Google Ads it steers your bid strategy in the wrong direction. If you have your measurement reviewed by a Google Analytics agency, this is where it starts.

Which actions do you mark as key events?

Only actions that are directly worth something to your business. Not every useful interaction is.

Use the event names Google recommends, because GA4 builds reports around them. For leads, those are generate_lead, qualify_lead, disqualify_lead, working_lead, close_convert_lead and close_unconvert_lead ^[2]. For a purchase, transaction_id and items are required; if you send a value, currency is required too ^[3].

Don't mark engagement. Some guides recommend "30 seconds on the page and 75% scrolled" as a key event. Such an event happens far more often than a lead, and as a primary conversion it teaches your bid strategy to find readers instead of customers.

You can mark a click on a phone number or email address, but it remains a weaker signal than a submitted form. Keep the number small: a standard property can have up to 30 key events ^[4], but the more you mark, the less "key events per session" still tells you.

How to make a key event fire reliably

A key event is only as reliable as the moment it fires. Have your website send an event to the data layer only once the form has actually been sent, and let Google Tag Manager pass it on to GA4. On izoard.be the contact form works like this: only once the form has reached the CRM does a generate_lead event go to the data layer.

A page view of the thank-you page is quicker to set up, but anyone who reloads the page or comes back to it later counts again. Only use it temporarily. For purchases, always send a unique transaction_id: GA4 deduplicates on it, but only for web streams and never with an empty value ^[5].

For each key event you also choose the counting method ^[6]:

• Once per event: the default for new key events and Google's recommendation. Logical for purchases, with the transaction ID as protection.
• Once per session: called "legacy" by Google and the default for migrated Universal Analytics goals. Sometimes more realistic for a form that visitors submit twice.

If you give your key events a value, you read your reports in euros. For a purchase that is the real order value; for a lead you set a default value ^[4]. Base it on what an average lead brings in, and write down how you arrived at it.

You mark an event with the star under Admin › Data display › Events. A new key event appears in the standard reports within 24 hours ^[4].

From key event to conversion in Google Ads

There are two routes. In GA4 you create a conversion from your key event under Advertising › Conversion management, or you fire the Google Ads conversion tag via Tag Manager at the same moment as your GA4 event.

For the first route, GA4 and Google Ads must be linked and auto-tagging must be on. Google sets such a conversion to secondary by default, precisely to avoid double counting in your bid strategy ^[7].

Whichever route you choose, three rules apply:

1. One primary source per action. Only primary actions count in the Conversions column and steer your bid strategy ^[8]. If a GA4 import and a Google Ads tag for the same lead are both set to primary, every lead counts twice.
2. A deliberate counting method. "Every" counts all conversions after a click, "One" counts one per click ^[8]. For leads "One" is usually more logical, for purchases "Every".
3. A known attribution model. Google Ads still offers data-driven attribution, the default for most conversion actions, and last click ^[9].

Why reliable conversions are the foundation of your campaigns is explained in Google Ads for SMEs: budget, approach and expectations. If you also want to link conversions to a click without a cookie, look at enhanced conversions in Google Ads.

Why GA4 and Google Ads show different numbers

Because they count differently, and that is usually not an error. Google Ads records a conversion on the day of the click, GA4 on the day of the conversion. Someone who clicks on 19 July and requests a quote on 20 July appears in Google Ads on 19 July and in GA4 on 20 July ^[8].

Google Ads also only gives credit to Google Ads, while GA4 includes all channels according to your attribution settings ^[10]. On top of that come the counting method, primary and secondary actions, filtered invalid clicks and an import delay of up to 24 hours ^[8].

All the causes are listed in Why GA4 and Google Ads show different numbers. So compare every month with your own source: the orders in your webshop or the requests in your CRM.

Not sure your key events are right? The free tracking audit checks whether the right actions are marked, whether they count once and whether the link with Google Ads causes double counting.