Data Streams

A data stream is a source of data flowing into a GA4 property. Every GA4 property needs at least one stream, and most need exactly one per platform: one web stream, one iOS stream, one Android stream.

Unlike Universal Analytics where tracking IDs (UA-XXXXXXXX-X) were tied to the property, GA4 separates the property from the stream. Your property has a property ID (a number like 123456789) and each stream has its own measurement ID (G-XXXXXXXXXX for web) or Firebase app ID for mobile.

Stream types

Web stream — collects data from browsers via gtag.js or Google Tag Manager. Identified by a measurement ID in the format G-XXXXXXXXXX.

iOS app stream — collects data from iOS apps via the Firebase SDK. Identified by a Firebase App ID.

Android app stream — collects data from Android apps via the Firebase SDK.

A GA4 property can have up to 50 data streams. You can combine web and app streams in the same property — GA4 is designed for cross-platform measurement, and having a single property for all platforms is the recommended approach.

Creating a web stream

1. Go to Admin → Data Streams → Add stream → Web.

2. Enter your website URL. GA4 will verify this during setup.

3. Enter a stream name — something descriptive like “Website - Production” or “[Brand] - Web”.

4. Toggle Enhanced Measurement on or off. You can change this later and configure individual events independently.

5. Click Create stream.

After creation, you will see:

• Measurement ID — the G-XXXXXXXXXX ID you add to your site tag or GTM
• Stream ID — a numeric identifier used in the API
• Enhanced Measurement settings — toggle individual auto-tracking events

Stream-level settings

From the stream details page:

Tag settings — Additional configuration for the gtag that deploys this stream, including:

• Session timeout (default: 30 minutes; range: 5 minutes to 7 hours 55 minutes)
• Engaged session timeout (default: 10 seconds)
• Default values for cross-domain tracking, cookie settings, and consent mode

Measurement Protocol API secrets — Required for sending data to GA4 via the Measurement Protocol. Each secret is a string added as the api_secret parameter in server-side calls.

Connected site tags — Link other tag IDs (UA or other GA4 property IDs) so a single gtag fires multiple properties.

Enhanced Measurement configuration

Enhanced Measurement auto-collects additional events beyond the base page_view. Toggle individual events in Admin → Data Streams → [stream] → Enhanced Measurement (gear icon).

Event	What it tracks	Default
Page views	page_view on each navigation	On
Scrolls	scroll at 90% page depth	On
Outbound clicks	click on external links	On
Site search	view_search_results on query param URLs	On
Video engagement	YouTube embedded video events	On
File downloads	file_download on file link clicks	On
Form interactions	form_start, form_submit (beta)	Off

Caution

Enhanced Measurement events come with significant caveats. Scroll only fires at 90% — you cannot get 25/50/75% granularity without custom implementation. Outbound clicks fire on any link to a different domain, including your own subdomains if you have not configured cross-domain tracking. Before relying on these events, read Enhanced Measurement Pitfalls.

Page view measurement in SPAs

For Single Page Applications (React, Vue, Angular, etc.), Enhanced Measurement cannot detect route changes automatically. A route change in a SPA does not fire a new page load — the browser URL changes but no HTTP request is made.

Configure your framework’s router to push a history change or fire page_view manually:

// After a route change in your SPA
gtag('event', 'page_view', {
  page_title: document.title,
  page_location: window.location.href,
  page_path: window.location.pathname
});

In GTM, use the History Change trigger and attach a GA4 Configuration or GA4 Event tag to it.

Cross-domain tracking

When users navigate between domains (e.g., from shop.example.com to checkout.example.com), GA4 treats each domain as a separate origin by default. The client_id cookie does not transfer, which breaks the session and creates a (direct) referral.

Configure cross-domain tracking at Admin → Data Streams → [stream] → Configure tag settings → Configure your domains.

Add all domains that should be treated as part of the same property:

• example.com
• shop.example.com
• checkout.example.com

GA4 will automatically add a _gl parameter to links between these domains, carrying the client_id across the transition.

Tip

Cross-domain tracking must be configured on every stream and domain in the relationship. If shop.example.com knows to link to checkout.example.com but checkout.example.com does not know to accept the parameter, the linking will not work.

iOS and Android app streams

For mobile apps, create separate streams for each platform. Each stream is linked to a Firebase project and app.

1. Go to Admin → Data Streams → Add stream → iOS app (or Android).

2. Enter the app bundle ID (iOS: com.company.app) or package name (Android: com.company.app).

3. Enter the app name.

4. Click Register app.

5. Download the GoogleService-Info.plist (iOS) or google-services.json (Android) configuration file.

6. Add the Firebase SDK and configuration file to your app.

Firebase SDK integration

The GA4 mobile SDK ships as part of Firebase Analytics. Add it to your app:

iOS (Swift)

// In AppDelegate or App struct
import FirebaseAnalytics

// Log an event
Analytics.logEvent(AnalyticsEventPurchase, parameters: [
  AnalyticsParameterTransactionID: "T-12345",
  AnalyticsParameterValue: 49.99,
  AnalyticsParameterCurrency: "USD"
])

Android (Kotlin)

import com.google.firebase.analytics.FirebaseAnalytics
import com.google.firebase.analytics.ktx.analytics
import com.google.firebase.analytics.ktx.logEvent
import com.google.firebase.ktx.Firebase

// Log an event
Firebase.analytics.logEvent(FirebaseAnalytics.Event.PURCHASE) {
  param(FirebaseAnalytics.Param.TRANSACTION_ID, "T-12345")
  param(FirebaseAnalytics.Param.VALUE, 49.99)
  param(FirebaseAnalytics.Param.CURRENCY, "USD")
}

Multiple streams vs. multiple properties

Use multiple streams in one property when:

• You want unified cross-platform reporting (web + iOS + Android for the same product)
• Your web and app serve the same users and you want to analyze their behavior together
• You want a single BigQuery export with all platforms

Use separate properties when:

• You have genuinely different products or brands that should be reported separately
• Different teams own different platforms and need separate access controls
• You have different data retention or compliance requirements per platform

Tip

For most businesses with a website and a mobile app serving the same product, one property with multiple streams is the right architecture. You get cross-platform user counts and unified funnels without data joins.

Measurement ID vs. Property ID

These are two different identifiers that are often confused:

Property ID — a numeric ID like 123456789. Used in the Admin API and for identifying the property in Google’s systems.

Measurement ID — a string like G-XXXXXXXXXX. This is what goes in your gtag.js or GTM GA4 Configuration tag. Only exists for web streams.

Stream ID — a numeric ID specific to the stream. Used in the Measurement Protocol API endpoint.

If you are adding GA4 to your site, you need the Measurement ID (G-XXXXXXXXXX), not the property ID.

Common mistakes

Using one property for staging and production

Do not mix staging and production data in the same GA4 property. Create a separate property for your staging environment. Production data contaminated with test data is difficult to clean up retroactively, and GA4 has no view-level filtering like Universal Analytics did.

Use a GA4 Data Filter to exclude developer traffic in your production property as a secondary protection, but the primary isolation should be separate properties.

Not configuring stream domains for cross-domain sites

If your checkout is on a separate domain from your marketing site, forgetting to configure cross-domain tracking will cause most of your checkout sessions to appear as direct traffic and your conversion rate to appear much lower than it actually is.

Missing the Measurement ID when using GTM

In GTM, the GA4 Configuration tag requires the Measurement ID (G-XXXXXXXXXX). It is easy to accidentally enter the property ID (a plain number) or the old UA format instead. Double-check the format — it must start with G-.

Related articles

Enhanced Measurement Pitfalls The specific problems with each Enhanced Measurement event and how to fix them.

Property Setup Property-level configuration including time zone, currency, and BigQuery linking.

Internal Traffic Filtering Use Data Filters to exclude developer and internal traffic from reports.

Measurement Protocol Send server-side events to a GA4 stream using the Measurement Protocol.