What is a key event in Google Analytics 4?
What counts as a key event?
An event is something GA4 records: a page view, a click, a purchase. Most of them are just activity. A key event is one you have told GA4 to treat as important, such as a purchase or a sign-up.
Marking is a choice. Nothing becomes a key event on its own. If the purchase event is not marked, it will not show up as one.
What happened to GA4 conversions?
A UK agency's 2024 blog post reports that Google renamed "conversions" in GA4 to "key events"3. The old and new names still turn up side by side in reports, tutorials and agency decks. That causes confusion.
Here is the split today. In Google Ads, a conversion is an action used to measure campaign performance and optimise bidding2. In GA4, an important action is a key event. A key event becomes a Google Ads conversion only if it is imported. Our convention: we say "key event" for GA4 and "conversion" for Google Ads, and we do not write "GA4 conversions" any more.
Why do GA4 and Google Ads show different totals?
The two systems have different counters. Each one decides what counts, which visits it sees and when credit is given. Both can be right by their own rules and still disagree.
So two different totals are not yet a problem. They become one when nobody can say why. Start with which key events are imported into Google Ads as conversions. Then compare the attribution window and the attribution model on each side. The credit rule, such as data-driven attribution, is part of that comparison.
For ZFD: We list every key event and every Google Ads conversion side by side. It is one of the checks in an ecommerce tracking audit. For where key events are marked and what GA4 does not collect by default, see what GA4 counts and what it doesn't.
Easily confused with
Key event vs Conversion
The Google Ads term for an action you value that follows an ad interaction. A GA4 key event may be imported into Google Ads as one, but they are counted separately.
Key event vs Event
Any recorded action. Only the ones you mark are key events.
Key event vs Session
A period of user activity. A session may contain a key event, or none.
FAQ
Is a key event the same as a conversion?
Almost. The idea is the same, but Google Ads Help says only conversions, not key events, are eligible for bidding and reporting in Google Ads2.
Can any event be a key event?
Yes. Any event GA4 collects can be marked as one1. Mark the ones that matter to the business, not everything.
Does a key event mean the ad caused it?
No. A key event records that something happened. Whether the ad caused it is a separate question, and no event count answers it.
Sources
Let’s find what’s actually working.
Next step. See what your conversion numbers look like on explicit assumptions. Use the Is your ROAS real? calculator.