Conversion tracking in GA4 works differently from Universal Analytics. UA had separately defined goals with distinct measurement types (destination, duration, pages per session, event). GA4 uses a simpler model: any event can be marked as a key event (conversion) with a single toggle. This simplicity introduces specific failure modes that are worth understanding before assuming your conversion data is accurate.
Setting up conversion tracking step by step
Mark the key event as a conversion in GA4 admin
Navigate to Admin > Events. Find the event you want to count as a conversion and toggle Mark as key event. GA4 counts this event from the moment you toggle it, it does not apply retroactively. If the event has not fired yet, create the event in Admin > Events first, then mark it as a key event.
Verify the event is firing correctly
Open GA4 DebugView and trigger the conversion action on your site or app. Confirm the event appears in the DebugView stream with the correct parameters. Check that event parameters (value, currency, transaction_id for purchases) are populated correctly.
Set the correct conversion counting method
In Admin > Events > Key events, review the counting method for each key event. For most modern GA4 key events, once per event is the default and recommended option. Once per session is a legacy option that may still appear on migrated setups. Choose the method that matches the business meaning of the event.
Link to Google Ads and import the conversion
In Admin > Product Links, confirm the GA4 property is linked to Google Ads. In Google Ads, go to Goals > Conversions > Import and import the key event from Google Analytics. Set the imported conversion action to Primary if you want Smart Bidding to optimise toward it.
How GA4 counts conversions
GA4 lets you count key events either once per event or once per session. For most key events created directly in GA4, once per event is the default and Google's recommended option. Older migrated setups may still use once per session.
For purchase events, GA4 also usestransaction_idto help prevent duplicate purchase counting in web streams. That is useful, but it is not a substitute for clean implementation design — seeduplicate transactions in GA4for the patterns that still slip through, andGA4 purchase event parametersfor the full list of fields you should be sending.
Choose the counting method by business meaning. If every lead form submission matters, once per event may be appropriate. If repeated actions in one session should count only once, once per session may be defensible.
Common key event misconfiguration: automatic events as conversions
The most consequential mistake in GA4 conversion setup: marking automatically collected or Enhanced Measurement events as key events. A fullGA4 custom events auditusually surfaces these issues alongside naming and parameter problems.
- page_view marked as conversion: Every session triggers a page_view. Marking page_view as a key event makes your conversion rate 100 percent. Every report that uses conversions becomes meaningless.
- scroll marked as conversion: 90 percent scroll depth fires on a large proportion of sessions for any content-heavy page. Marking scroll as a conversion inflates conversion numbers to many times their legitimate value.
- session_start marked as conversion: Every session triggers session_start. Marking it as a key event is identical to using sessions as the conversion metric.
Check Admin > Events. Every event with Mark as key event toggled on should represent a specific, meaningful business outcome.
Want to check whether your conversion events are configured correctly?
Google Ads conversion import
When GA4 is linked to Google Ads, you can import GA4 key events as conversion actions in Google Ads. This allows Google Ads Smart Bidding to optimise for the conversions you have defined in GA4. Confirm the property is set up correctly first using theGA4 property configuration checksguide.
- The key event must be firing correctly in GA4
- The GA4 property must be linked to Google Ads in Admin > Product Links
- The key event must be imported in Google Ads under Goals > Conversions > Import from Google Analytics
- The imported conversion action must be set to Primary (not Secondary) if you want Smart Bidding to use it
Do not import the same conversion into Google Ads both from GA4 and via a separate Google Ads conversion tag. This creates duplicate conversion counting in Ads, which Smart Bidding will optimise toward, producing overbidding.
Conversion tracking checklist
- Only meaningful business outcomes are marked as key events (not page_view, scroll, or session_start)
- Conversion counting method (once per session vs once per event) is set correctly for each key event
- Purchase events use transaction_id deduplication correctly
- GA4 key events imported to Google Ads are set as Primary conversion actions for Smart Bidding
- No duplicate conversion tracking (GA4 import plus separate Google Ads tag for the same conversion)
- Key event counts validated in DebugView for a test conversion
- GA4 and Google Ads conversion totals understood to differ by design, not compared directly
Related guides to read next
GA4 Attribution Models Explained
How GA4 data-driven attribution works and how to compare it with last-click for accurate reporting.
GA4 Audit Checklist
A complete weekly monitoring routine covering all 8 GA4 audit areas systematically.
Why GA4 Numbers Don't Match Google Ads
The structural reasons GA4 and Google Ads report different conversion and session counts.
GA4 Ecommerce Tracking Checks
How to validate purchase events, revenue parameters, and transaction deduplication in GA4.
Validate your GA4 conversion tracking automatically
GA4 Audits checks key event configuration, counting methods, Google Ads import status, and duplicate conversion risks across your property.