What Is Google Analytics? What GA4 Does and Why Advertisers Need It

What is Google Analytics? Google Analytics is Google's analytics tool that measures where visitors to your website and app come from, what they do and whether they convert. Its current version is GA4; the previous version, Universal Analytics, stopped processing data on July 1, 2023. The standard version has no license fee; a paid GA4 360 edition exists for large organizations.

For advertisers, GA4's most important role is to be common ground that shows every channel on the same yardstick, independent of the reports inside Google Ads, Meta or TikTok. Each platform credits its own touchpoints; GA4 compares site traffic under a single attribution logic.

How does GA4 work?

GA4 collects user interactions through the Google tag (or Google Tag Manager) on your site. Unlike Universal Analytics' session and page view model, GA4 is event-based: page views, scrolls, clicks, form submissions, add-to-carts and purchases are all events. Events that matter to your business are marked as 'key events' (Google renamed 'conversions' this way in 2024).

• Automatic events: page view, session start, first visit and similar events come with setup.
• Enhanced measurement: scrolls, outbound clicks, site search and video engagement switch on with one toggle.
• Recommended and custom events: ecommerce events (view_item, add_to_cart, purchase) and business-specific events are added via code or GTM.
• Key events: business goals such as sales, forms or calls; they can be imported into Google Ads for bidding.

Which GA4 reports should advertisers look at?

GA4's standard reports fall under four headings: acquisition (where traffic comes from), engagement (what people do on site), monetization (revenue and ecommerce) and retention (whether users come back). The most valuable for advertisers is traffic acquisition: sessions by default channel group, source/medium and campaign.

• Traffic acquisition: sessions, engagement rate and key events by channel, source and campaign.
• Monetization: revenue, purchases, average purchase revenue and product performance.
• Explorations: an open canvas for funnel, path and segment analysis (GA4 explorations guide).
• Advertising section: attribution model and conversion path comparisons.

How do you set up Google Analytics?

1. Create an account and a GA4 property at analytics.google.com; set time zone and currency correctly.
2. Add a web data stream and place the Google tag on your site, either directly or via Google Tag Manager.
3. Turn on enhanced measurement, then mark events such as sales or forms as key events.
4. Raise data retention to 14 months, the longest option in the standard version; the default is 2 months.
5. Link your Google Ads account and use UTM parameters consistently on ad links (UTM guide).

How long does GA4 keep data?

GA4's data retention setting controls how long event-level data stays available in explorations. In the standard version the options are 2 or 14 months, and the default is 2, so raising it to 14 right after setup matters. GA4 360 extends retention to up to 50 months. Aggregated data in standard reports is not affected by this setting; for longer raw data, use the BigQuery export.

Common Google Analytics setup mistakes

• Leaving retention at 2 months: you lose historical comparison in explorations.
• Double tagging: adding the tag both in code and in GTM counts sessions and events twice.
• Ad links without UTMs: paid social traffic disappears into 'direct' or 'referral'.
• Not excluding your own traffic: office and agency visits distort conversion rate; define an internal traffic filter.
• No value on the purchase event: revenue and ROAS reports stay empty (check with explorations).

How does Ads Sensor use GA4 data?

Ads Sensor reads your GA4 property in the same panel as your Google Ads, Meta, TikTok and Criteo accounts. It shows GA4 traffic, conversion and channel breakdowns next to each ad platform's own reports so the gaps become visible, and its AI analysis folds on-site behavior signals into campaign recommendations. You no longer have to open GA4 in another tab and compare by hand. Apply for the beta.