Which Google Ads conversion action do you set as primary?

When setting up Google Ads conversions via Server-Side Tagging, we regularly encounter this question: “Which conversion action should I set as primary?”. It's an important question, as the choice directly impacts the optimisation of your campaigns. In this article, we explain how to make the best choice.

Een Google Ads conversieactie is een specifieke, waardevolle actie die een klant onderneemt nadat hij op een van uw advertenties heeft geklikt.

Google Ads conversion actions are a way to measure whether important user interactions on your website have taken place thanks to your Google Ads campaigns. These include purchases, completed forms, or downloads. Google Ads has different categories of conversion actions, each representing a specific type of user action:

• Purchase/SaleFor e-commerce transactions
• LeadFor the collection of potential customer data
• Add to basketFor tracking products in shopping baskets
• Begin checkoutTo start the checkout process
• SubscriptionFor service registrations
• Request for quotationFor requesting quotes
• App installationFor downloading mobile apps
• Display of important pageFor visits to specific pages
• OtherFor other valuable actions that do not fit into the above categories

The choice of category is important as Google Ads uses this information to determine the bidding strategy. You select one of these categories for your campaigns, and the Google Ads algorithm will use your selection to implement a bidding strategy. This only happens based on primary conversion actions; secondary conversion actions do not influence the bidding strategy.

These conversion actions within the conversion categories can be measured in different ways:

• Via the Google Tag Manager web container (client-side)
• Via Server-Side Tagging
• Via a GA4 import
• Via een direct script op de website
• Via de AdPage Google Ads API tag

Each method has its own advantages and disadvantages, which we will discuss later in the blog post.

Google Ads verwerkt conversiedata door middel van tags die op uw website worden geplaatst of door gegevens te importeren. Deze tags volgen gebruikersacties die u als waardevol beschouwt, zoals aankopen of aanmeldingen. Wanneer een gebruiker een conversie voltooit, worden de gegevens naar Google Ads verzonden. Google gebruikt vervolgens deze gegevens om de prestaties van uw advertenties te meten en te optimaliseren, zodat u beter inzicht krijgt in welke advertenties leiden tot waardevolle acties.

Google Ads uses various Attribution models to determine which adverts have contributed to a conversion. Unlike GA4, which uses last-click attribution, Google Ads can assign conversions over a longer period and multiple sessions. This means a conversion in Google Ads can be attributed to adverts without you being able to see it in your GA4 property or in the backend of your CMS.

Click-through and view-through attribution

Google Ads uses two types of attribution:

Click attributionThis assigns conversions to ads that users have clicked on. Google Ads offers several attribution models:

• Last click: 100% of the conversion value goes to the last click
• First click: 100% of the conversion value goes to the first click
• Linear: The conversion value is distributed equally across all clicks
• Time decay: Recent clicks are worth more than older clicks
• Position-based: 40% for first click, 40% for last click, 20% distributed over intermediate clicks
• Data-driven: An advanced model that uses machine learning to determine optimal attribution

View-through attributionEven without direct interaction with your ad, Google Ads can attribute a conversion if the visitor has merely seen it. This is measured within a configurable view-through conversion window (the default is one day).

Impact on reporting

This attribution difference has some important consequences:

• One conversion can be attributed to multiple ads
• Conversion volumes in Google Ads can be higher than those attributed in GA4 or your CMS
• View-through conversions can lead to additional claimed conversions
• The chosen attribution model has a direct impact on the optimisation of your campaigns

It is therefore important to:

• To consciously choose your attribution model based on your marketing strategy
• Conversion windows to align with your sales cycle
• Taking into account differences between different measurement methods

The different measurement methods compared

Client-side Google Tag Manager

You can set up a Google Ads conversion tag on the Google Tag Manager container based on a trigger that's activated by a specific site interaction. The advantage of this traditional method of measuring conversions is that it's relatively simple to implement. Disadvantages include:

• Sensitive to ad blockers
• Less accurate for cross-device conversions
• Cookie-dependent
• Takes place entirely in the visitor's browser

Server-side Google Tag Manager

Server-Side Tagging is the implementation of a Google Ads conversion tag on the sGTM container at the moment a specific event enters your server container. This method is often seen as the “best” solution, but that's not always the case:

• Advantages: less sensitive to ad blockers and better control over data.
• Disadvantages: gbraid and wbraid parameters are not always correctly passed for Apple users and differences in the processing of enhanced conversions.

GA4 import

A direct connection is possible between GA4 and Google Ads. When you link your GA4 conversions to Google Ads, the Google Ads algorithm has more data to work with than via standard Google Ads conversion tags on Google Tag Manager containers. For businesses working with webhooks, the GA4 import conversion action will almost always perform better.

• Benefits: works well with webhook implementations and is consistent with your GA4 data
• Disadvantages: attribution model differs from native Google Ads tracking and data processing delay

Direct script

Placing the Google Ads global site tag (gtag.js) directly on your website is one of the basic methods for measuring conversions. The implementation consists of two parts: placing the Global Site tag script on every page of your website, and a specific code that is only placed on the conversion page.

• Advantages: fast data processing in Google Ads
• Disadvantages: limited flexibility with customisations, sensitive to ad blockers, difficult to debug and no central tag management possible

AdPage Google Ads API tag

This specific solution only works with AdPage webhooks. We developed this tag ourselves because the standard server-side Google Ads conversion tags do not consistently forward the gbraid and wbraid parameters from Apple users.

• Advantages: highly reliable for webhook-based conversions, not affected by ad blockers, optimised for server-side implementations, and Apple users can be tracked as gbraid- and wbraid- parameters can be sent along.
• Disadvantages: only works with AdPage webhooks and requires specific setup

How do you determine which Google Ads conversion action is performing best?

By ‘best performing’ we mean 'which conversion action is the most accurate', which is technically the conversion action that makes the most data available to Google Ads so that Google Ads can claim the most conversion actions. So if one of your conversion actions is measuring more than double compared to the others, it might also be that you are sending double data. This is a situation you should avoid so you don't make budget or marketing decisions based on results that appear twice as good as they actually are. To determine which conversion action is the most accurate, it's best to follow these steps:

1. Compare the conversion numbers over a specific period between:

• Google Ads
• GA4
• My CMS/backend system

2. In GA4, specifically look at:

• The number of conversion events
• The session source/medium as a dimension
• Please note: GA4 only shows last-click attribution

3. Check in Google Ads:

• The different conversion actions
• The attribution model
• The time between click and conversion

Which conversion action do you choose as primary?

The choice of a primary conversion action depends on several factors:

Do you use webhooks? If so, consider the GA4 import or the AdPage Google Ads API tag. The standard Google Ads tag cannot work with webhooks.

Do you have many Apple users? Please note the processing of gbraid and wbraid parameters. The Server-Side Tagging conversion action is not always the best choice for sites with many mobile Apple users.

3. Which attribution model is best suited? GA4 import uses last-click and native Google Ads conversion actions can use different models.

4. Technical setup Which implementation best suits your infrastructure? How important is Server-Side Tagging for your situation?

Conclusion

There is no “one size fits all” solution for choosing a primary conversion action. It depends on your specific situation, technical setup, and target audience. Measure and compare the different methods over a period of at least one month to see which performs best for your situation. In any case, do not be constantly switching your primary conversion action; make the choice once after a Server-Side Tagging implementation.

Key considerations include:

• The reliability of the measurements
• The completeness of the data
• The way conversions are attributed
• The technical implementation and maintenance

By carefully weighing these factors, you can make an informed choice for your primary conversion action in Google Ads.