What Google Ads conversion action do you put on primary?

Tobias Pennings
March 7, 2025
Overview
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When setting up Google Ads conversions via Server-Side Tagging, we frequently come across this question, "Which conversion action should I set as primary?". It's an important question, because the choice directly affects the optimization of your campaigns. In this article, we explain how to make the best choice.

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What is a Google Ads conversion action?

Google Ads conversion actions are a way to measure whether key site interactions of users on your website have been carried out thanks to your Google Ads campaigns. Examples include a purchase, a form completion or a download. Google Ads has several categories of conversion actions, each representing a specific type of user action:

Purchase/Sale: For e-commerce transactions

Lead: For collecting potential customer data

Add to cart: For tracking products in shopping carts

Start of checkout: For starting the checkout process

Subscription: For subscriptions to services

Quote Request: To request price quotes.

App installation: For downloading mobile apps

Display of important page: For visits to specific pages

Other: For other valuable actions that do not fit into the above categories

Conversion action categories in Google Ads

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The choice of category is important because Google Ads uses this information to determine the bidding strategy. This is because you select one of these categories in your campaigns, and Google Ads' algorithm is going to use a bidding strategy based on your choice. This only happens based on the primary conversion actions, secondary conversion actions do not affect the bid strategy.

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

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

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How does Google Ads process conversion data?

Google Ads uses different attribution models to determine which ads contributed to a conversion. Unlike GA4, which uses last-click attribution, Google Ads can attribute conversions over a longer period of time and multiple sessions. This means that a conversion in Google Ads can be attributed to ads without being able to see it in your GA4 property or in the backend of your CMS.

Click and view-through attribution

Google Ads uses two types of attribution:

Click attribution: This involves assigning 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 get more value than older clicks
  • Position-based: 40% for first click, 40% for last click, 20% spread over intermediate clicks
  • Data-driven: An advanced model that uses machine learning to determine optimal attribution

View-through attribution: Even without direct interaction with your ad, Google Ads can claim a conversion if the visitor only saw it. This is measured within an adjustable view-through conversion window (default is one day).

How GA4 and Google Ads can show differences in conversion sources thanks to view-through conversions

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Impact on reporting

These attribution differences have some important implications:

  • One conversion can be assigned to multiple ads
  • Conversion numbers in Google Ads may be higher than they are assigned in GA4 or your CMS
  • View-through conversions can lead to additional claimed conversions
  • The attribution model you choose directly affects the optimization of your campaigns

It is therefore important to:

  • Choose your attribution model consciously based on your marketing strategy
  • Align conversion windows with your sales cycle
  • Take into account differences between different measurement methods

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The different measurement methods compared

Client-side Google Tag Manager

On the Google Tag Manager container, you can set up a Google Ads conversion tag based on a trigger that activates on a specific site interaction. This traditional way of measuring conversions has the advantage of being relatively easy to implement. Disadvantages are:

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

Server-side Google Tag Manager

Server-Side Tagging is setting a Google Ads conversion tag on the sGTM container the moment a specific event comes in on your server container. This way is often seen as the "best" solution, but that is not always the case:

  • Advantages: less prone to adblockers and better control over data.
  • Disadvantages:gbraid and wbraid parameters are not always passed correctly for Apple users and differences in 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 through the standard Google Ads conversion tags on the Google Tag Manager containers. For companies working with webhooks, the GA4 import conversion action will almost always perform better well.

  • Advantages: works well with webhook implementations and consistently with your GA4 data
  • Cons: attribution model differs from native Google Ads tracking and delay in data processing

Direct script

Placing the Google Ads global site tag (gtag.js) directly on the 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 placed only on the conversion page.

  • Benefits: fast data processing in Google Ads
  • Disadvantages: little flexibility in customization, sensitive to adblockers, difficult to debug and no central tag management possible

AdPage Google Ads API tag

This particular solution only works with AdPage webhooks. In fact, we developed this tag ourselves because the standard server-side Google Ads conversion tags do not consistently forward Apple users' gbraid and wbraid parameters.

  • Advantages: highly reliable for webhook-based conversions, no problems with adblockers, optimized for server-side deployments and allows Apple users to track as gbraid and wbraid parameters can be sent along
  • Cons: works only with AdPage webhooks and requires specific setup
Case study where multiple conversions are set to primary, but the best performing one is set as secondary

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How do you determine which Google Ads conversion action performs best?

By best performing, we mean "which conversion action is most accurate," which is technically the conversion action that makes the most data available to Google Ads so Google Ads can claim the most conversion actions. So if one of your conversion actions measures more than double compared to the other, you may also be sending duplicate data. This is a situation you need to avoid so you don't start making budget or marketing decisions based on results that look twice as good as they really are. To determine which conversion action is most accurate, it is best to follow the following steps:

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

  • Google Ads
  • GA4
  • Your CMS/backend system

2. In GA4, look specifically at:

  • The number of conversion events
  • The session source/medium as a dimension
  • 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

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Which conversion action do you choose as primary?

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

1. Are you using webhooks? If so, consider the GA4 import or the AdPage Google Ads API tag. The default Google Ads tag cannot work with webhooks.

2. Do you have many Apple users? Pay attention to 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 fits best? GA4 import uses last-click and native Google Ads conversion actions can use different models.

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

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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 different methods over a period of at least a month to see which one performs best for your situation. In any case, do not make sure you are constantly switching primary conversion action, make the choice once after a Server-Side Tagging implementation.

Important considerations are:

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

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