If you set up GA4 before 2024, you marked events as "conversions". Log in now and the same toggle says "key event". Nothing about your tracking changed. The rename was about separating two things that had been sharing one word.
This guide explains what each term means, how they connect, and why GA4 and Google Ads almost never show the same number.
What changed in March 2024.
Google renamed conversions in GA4 to key events in March 2024. Every event you had marked as a conversion became a key event automatically, with the same data and history.
The reason was confusion. GA4 and Google Ads both said "conversions" but counted them in different ways, so the same word gave two different numbers. Google now uses "conversion" for what Google Ads counts, and "key event" for what GA4 measures.
You'll still see "conversions" inside GA4 in places tied to advertising, such as the reports on Google Ads performance. That's deliberate: those figures follow Google Ads rules.
What a key event is in GA4.
A key event is any GA4 event you've flagged as important to the business. The event itself is ordinary: purchase, generate_lead, sign_up or a custom event such as book_demo. Marking it as a key event tells GA4 to count it in key event reports and use it in attribution.
You mark events in Admin, in the events list under Data display, by switching on the key event option. You can also create a key event for an event that hasn't fired yet by typing its exact name.
Key events have a counting method. The default counts every time the event fires. You can change it to once per session, which suits leads where a second form submission in one visit isn't a second lead.
What a conversion is in Google Ads.
A conversion in Google Ads is a conversion action: something Ads counts, credits to its own ads, and can use for bidding. Each action has its own settings: a value, a counting method (one or every), a click-through conversion window, and an attribution model.
Google Ads only credits conversions to its own ad interactions. It doesn't care about organic search, email or social, except where they shape how credit is shared under data-driven attribution.
How a key event becomes a Google Ads conversion.
There are two routes. Most accounts use one or the other for each action.
- Import from GA4. Link GA4 and Google Ads, then in Google Ads create a new conversion action and choose to import from your GA4 property. Only key events are available to import. Imported data can take some hours, sometimes a day or more, to appear in Ads.
- The Google tag. Send the conversion straight to Google Ads using the Google tag or a Google Ads conversion tag in GTM, with the conversion ID and label. This is faster and doesn't depend on GA4, but it's a second piece of tracking to maintain.
Neither route is wrong. Importing keeps one definition of each action. The Google tag gives Ads its own data, which suits accounts that need enhanced conversions or fast feedback for bidding.
Primary and secondary conversions in Google Ads.
Every conversion action in Ads is either primary or secondary.
- Primary actions appear in the Conversions column and are used for bidding, if the campaign's goals include them.
- Secondary actions appear only in the All conversions column. They're for observation and don't affect bidding.
Use primary for the outcomes you'd pay for: purchases, qualified leads, booked calls. Keep micro actions such as add to basket or newsletter sign-ups as secondary, unless there's a deliberate reason to bid on them.
A quick comparison.
| GA4 key event | Google Ads conversion | |
|---|---|---|
| Where it lives | GA4 property | Google Ads account |
| Credits | All channels | Google Ads interactions only |
| Reported on | The date the event happened | The date of the ad click, in most reports |
| Counting | Once per event or once per session | One or every, per action |
| Used for bidding | No | Yes, if primary |
Why GA4 and Google Ads show different numbers.
Expect a gap even when everything is set up correctly. The usual reasons:
- Attribution. GA4 shares credit across every channel. Ads only counts conversions it can link to its own clicks or views, so GA4 gives some of the credit Ads claims to organic, email or direct.
- Click date versus conversion date. Google Ads reports a conversion against the date of the ad click. GA4 reports it on the day it happened. A click on the 30th that converts on the 2nd lands in different months.
- Counting once versus every. An Ads action set to "one" counts one conversion per click. A GA4 key event counting every event can record several.
- Conversion windows. Ads counts conversions within the action's window after a click, 30 days by default. GA4 has its own lookback windows in its attribution settings. Different windows mean different totals.
- Cross-device and view-through. Ads can count conversions from signed-in users across devices, and from views of video or display ads. GA4 doesn't see all of that.
- Consent. Where users decline cookies, Consent Mode lets Google model some of the missing conversions. Ads and GA4 model in different ways and to different thresholds, so modelled totals differ too.
How to diagnose it: Compare like with like. Filter GA4 to Google Ads traffic, use the same date range, and remember Ads is reporting by click date. If the numbers are still far apart for the same action, look for a tracking fault rather than a reporting difference.
How many key events to have, and which.
A standard GA4 property allows a limited number of key events (currently 30 in standard properties), but you should need far fewer. A handful is typical. Every extra key event makes the reports noisier and the attribution harder to read.
Choose actions that represent real value:
- Ecommerce:
purchase. Maybebegin_checkoutif you use it to judge campaigns. - Lead generation: a submitted enquiry form, a booked call, a phone call click if calls matter to the business.
- SaaS:
sign_upor a trial start, and a paid subscription if you can track it.
Engagement actions like scrolls, video plays and file downloads are useful as ordinary events. They rarely deserve key event status.
Common mistakes.
Marking page_view or session_start as a key event. Every visit becomes a "success", conversion rates hit 100% and attribution becomes meaningless. How to fix it: Unmark them. If a specific page matters, create a dedicated event for it, such as a thank-you page view, and mark that instead.
Counting form views instead of form submissions. An event that fires when a form loads, or when someone starts typing (form_start), isn't a lead. How to fix it: Fire the key event only on a confirmed submission: a thank-you page, a success message or the form's own success callback.
Duplicates. The same action counted twice: GA4 installed twice, a trigger firing twice, or an imported key event and a Google tag conversion both set as primary in Ads. How to diagnose it: Check the Ads conversions list for two primary actions measuring the same thing. The duplicate key events guide covers the GA4 side.
Assuming a key event is a conversion. Marking something as a key event in GA4 doesn't send it to Google Ads. Until it's imported, or tracked with the Google tag, Ads can't see it or bid on it.
Summary.
Key events are GA4's measure of what matters. Conversions are what Google Ads counts and bids on. You connect them by importing key events into Ads or tracking the action with the Google tag, and you choose which ones are primary.
Some gap between the two is normal. A large gap for the same action usually means duplicate or broken tracking.
If you'd rather have it checked, the GA4 mini audit covers your key events, how they reach Google Ads, and whether each one is counting what you think it is.