The ad_impression event
ad_impression is a GA4 event used to record that an ad was shown, most commonly in mobile apps monetised through ad mediation. It can carry ad_platform, ad_source, ad_format, ad_unit_name, and a value/currency representing estimated revenue. It is distinct from internal view_promotion: ad_impression is about third-party ad inventory served in your app, not your own merchandising slots.
What this means
ad_impression is a GA4 recommended event geared toward app monetisation. When an ad is served — typically via a mediation SDK such as those integrated with Google's mobile ads — the app sends ad_impression so revenue and supply can be analysed in GA4.
It is not for measuring your own promotional banners; those use view_promotion. ad_impression specifically represents third-party ad inventory.
Ad parameters
The event accepts ad_platform, ad_source, ad_format, and ad_unit_name to describe the impression, plus value and currency for estimated revenue. Because mediation SDKs can populate these automatically, ad_impression often flows without manual instrumentation in app contexts.
- ad_platform / ad_source: the serving stack
- ad_format / ad_unit_name: placement details
- value + currency: estimated impression revenue
How it appears in analytics and logs
An ad_impression event means a monetisable ad was displayed. Aggregated, it indicates ad-supply volume and, with value populated, estimated ad revenue.
Diagnostic use case
Measure ad impressions and estimated ad revenue in apps monetised through ad networks and mediation SDKs.
What WebmasterID can help detect
WebmasterID focuses on first-party site and app analytics; ad_impression illustrates how GA4 separates served-ad events from on-site promotions.
Common mistakes
- Using ad_impression for internal banners instead of view_promotion.
- Reporting estimated ad revenue as confirmed paid revenue.
- Expecting ad_impression to populate automatically on the web.
Privacy and accuracy notes
Ad parameters describe the placement and platform, not the user. Estimated revenue is a number, not personal data. Educational, not legal advice on ad regulation.
Related pages
- The ad_click event
ad_click represents a user interacting with a served advertisement. In GA4's model it is the click counterpart to ad_impression for third-party ad inventory, just as select_promotion pairs with view_promotion for internal merchandising. This page clarifies which click event belongs where so you do not conflate paid ad interactions with on-site promotion clicks or generic outbound link clicks.
- The view_promotion event
view_promotion is a GA4 recommended e-commerce event for internal merchandising. You fire it when a promotion — a banner, hero slot, or campaign creative inside your own site — becomes visible. It carries promotion_id, promotion_name, creative_name, and creative_slot, plus an items array. Paired with select_promotion, it measures the on-site impact of promotional placements distinct from external ad campaigns.
- Recommended vs custom events
GA4 events come in three tiers: automatically collected, recommended, and custom. Automatic events fire without setup; recommended events have Google-defined names and parameters that unlock standard reports; custom events are ones you invent. The practical rule is to prefer a recommended name whenever one fits, because custom names miss out on prebuilt dimensions, reports, and predictive features.
- Event Explorer
Inspect ad and monetisation events.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.