Conversion tracking from scratch: Google Ads, GA4 and Meta Pixel

Google Ads and Meta ads are run by algorithms now. They decide who sees your ad and how much to pay for a click, but only based on the data you give them. If they don't know who sent an enquiry or made a purchase, they optimise for clicks, and clicks don't pay the bills.

That's why conversion tracking is the first thing we check on every account. In this article we walk through the basic setup every business investing in ads should have.

1Decide what a conversion is for you

Before any technical setup, write down which actions on your site are actually worth something. For an online shop, that's a purchase. For a service business, it's a sent enquiry, a phone call or a WhatsApp message.

You can track smaller steps alongside your main conversions, such as add to basket or newsletter signups. What matters is that the algorithms optimise towards the main ones, not towards everything that can be measured.

2Set up Google Tag Manager

Google Tag Manager (GTM) is a single place to manage all your tags: GA4, Google Ads, Meta Pixel and the rest. The code goes on your site once, and everything else is edited in GTM, without touching the site's code.

That means fewer mistakes, faster changes and a clear view of what's being tracked on your site.

3GA4 and key events

Google Analytics 4 shows you the full picture: where visitors come from, what they do on your site and which channels bring in enquiries. In GA4, conversions are called key events.

Create an event for each important action, for example `generate_lead` for a sent form or `purchase` for a sale, and mark it as a key event. For forms, the most reliable approach is to fire the event on the thank-you page or after a successful submission, not on the button click itself.

4Conversions in Google Ads

You can give Google Ads conversions in two ways: through its own Google Ads tag, or by importing key events from GA4. Both work, but choose one as Primary. If both are primary, the same conversion is counted twice.

Alongside that, set up:

the Conversion Linker tag in GTM, so ad clicks are correctly linked to conversions,
Enhanced conversions, which, with the user's consent, improve measurement accuracy when cookies aren't available.

5Meta Pixel and the Conversions API

Meta Pixel tracks actions in the browser, but ad blockers, privacy settings and browsers stop it more and more often. That's why Meta also recommends the Conversions API, which sends the same events directly from a server.

When you use both, give each event the same `event_id`, so Meta recognises them as one and doesn't count them twice. Use standard events such as Lead and Purchase, and verify your domain in Business Manager.

6Consent: Consent Mode v2

Under UK GDPR and PECR, non-essential tracking cookies can only be set once a visitor has given consent. Your site needs a cookie banner with equally clear options to accept and reject.

For users in the UK and the European Economic Area, Google also requires Consent Mode v2. Your tags then know whether the user has consented and behave accordingly. Without it, you lose part of your measurement and remarketing features in Google Ads.

7Test before you launch any campaigns

Set up doesn't mean set up correctly. Before you spend your first pound, make a test conversion and check that it's recorded everywhere:

GTM Preview (Tag Assistant) shows which tags fire,
GA4 DebugView shows events in real time,
Meta Events Manager, under Test events, shows Pixel and Conversions API events,
in Google Ads, the conversion status should change to "Recording conversions" within a few hours.

Once your campaigns are live, compare the numbers once a week with the enquiries and orders you actually receive. Small differences are normal; large ones are a sign that something isn't working.

Checklist

You've written down which actions are your main conversions.
All tags fire through Google Tag Manager.
Your main actions are marked as key events in GA4.
In Google Ads, each conversion is set as Primary only once.
Meta Pixel and the Conversions API send the same events with the same event_id.
The cookie banner and Consent Mode v2 work before any tag fires.
A test conversion shows up in GA4, Google Ads and Meta Events Manager.

If this sounds like a lot of work, you're right: good tracking takes time to set up. But it's the only way to know which ads are actually selling. If you'd like us to check your setup, get in touch for a free audit.