Before ads, define what a conversion is for you (an inquiry, a call, a booking, a purchase), set it up in GA4 as a key event, introduce valid consent with Consent Mode v2 and test that each action is counted exactly once.
What a conversion actually is for your business
For a webshop it is a purchase. For a service company it is a submitted form, a call, a click on an email address, a booked appointment or a price list download. Write a list of actions that lead to money and rank them by importance.
Setting up GA4
- Mark the events you want to track as key events. They used to be called conversions.
- For a form, track the thank you page view or a direct submit event, but not both.
- For phone calls from mobile, track the click on the phone link. For calls coming from ads there is also separate call measurement in Google Ads.
- Link GA4 with Google Ads so that conversions can be used for optimization.
Consent Mode v2 and consent
If you have visitors from the European Economic Area and use Google's advertising features, you need valid consent and correct sending of consent signals. Consent Mode v2 adds two parameters, ad_user_data and ad_personalization, alongside ad_storage and analytics_storage.
In practice this means that before consent the tools do not set cookies, and after a decline or an accept the signal is sent to Google. There are basic and advanced implementations, and the difference is that the advanced one sends anonymized signals even before consent, which enables partial conversion modeling. This is a legal and technical area, so check the settings with a lawyer.
How to check that everything works
- In GA4 turn on DebugView and perform an action, for example submit a test form.
- Use Google Tag Assistant to see which tags fire and with which consent state.
- Check that the event does not fire twice, which often happens when the tag is set up both in the theme and in the tag manager.
- After launching the campaign, compare the number of conversions in Ads and GA4. Small differences are normal, big ones are not.
Common mistakes
- Counting every refresh of the thank you page as a new conversion.
- Measuring only the form, and not calls and clicks on email.
- A cookie banner that is displayed but does not send a real signal to the tools.
- No testing after a theme or plugin change on the website.
Frequently asked questions
Do I have to have a cookie banner?
If you use analytics or advertising cookies for visitors from the EU, valid consent is required. This is not legal advice, so check with a data protection expert.
What are key events in GA4?
These are the events you mark as important for the business. What used to be conversions in GA4 are now called key events.
How long does it take to set up measurement?
For a smaller website it is usually a few hours to a few days, including testing. Larger webshops need more time.
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