What Is GA4? Features, Measurement and Getting Started

April 8, 2026

Author: Shusaku Yosa

Google Analytics 4 (GA4) is Google’s analytics service for measuring activity on websites and apps. It collects actions as events and helps answer three practical questions: where visits came from, what people used, and whether they completed an important action.

Installing GA4 does not automatically reveal every visitor, every business outcome, or the additional revenue caused by advertising. Reliable analysis starts with a measurement plan and an understanding of the limits of the data.

What can you use GA4 for?

Business question	Useful report or tool	Possible action
What brings visits to the site?	Traffic acquisition and Landing page	Improve a channel and landing-page combination
Which content is being used?	Pages and screens	Add useful next steps to popular pages
Where does a journey break down?	Key events and explorations	Investigate a form or checkout step
Does the experience vary by device?	Device comparisons	Check a mobile-specific usability problem

Web and app data can be collected through the appropriate data streams. This does not guarantee perfect identification of the same person across devices. Consent, identifiers, sign-in behavior and configuration affect what can be connected.

Events, sessions and users are different units

An event records an action. A session groups activity according to session rules. A user count depends on the identifiers and reporting definitions available to GA4. An event count is therefore not a headcount.

Consider a hypothetical visitor who reads an article, opens a service page, starts a form and successfully sends an inquiry during one visit.

Action	Example measurement	What to check
Opens two pages	Two page_view events	Each page should be counted once
Begins a form	form_start	Collection depends on the form and settings
Successfully submits an inquiry	generate_lead	Implement and test a success-based trigger

Recommended event names do not implement themselves. Understand which events are automatically collected, which depend on enhanced measurement, and which need explicit implementation. Mark business-critical events as key events. Using them as Google Ads conversions is a separate configuration decision.

What GA4 cannot tell you on its own

Consent choices, browser behavior and missing tags can leave activity unobserved.
Reported users are not necessarily distinct real people.
User-, session- and event-scoped traffic-source dimensions answer different questions.
Attribution in a report is not proof of incremental advertising impact.
Sales, customer quality and gross profit after an inquiry require business records beyond website events.

When reports disagree, align the date range, time zone, filters and metric definitions first. Standard reports, explorations and exports can also differ in processing and reporting conditions. Exporting a CSV does not remove those differences.

A practical path from setup to analysis

Write one business question, such as whether content helps generate qualified inquiries.
Create the property and data stream, then install the Google tag.
Use Tag Assistant and DebugView to check normal browsing and important actions.
Configure key events, review internal traffic and remove duplicate event triggers.
Review a consistent set of metrics each week and record an action, owner and review date.

Start with sessions, landing pages and key events. Advanced exploration and predictive features have requirements and should support a specific decision. If you use BigQuery, also consider the costs of storage and querying in that service; an analytics integration does not make all associated services free.

A short note on Universal Analytics

Older Universal Analytics documentation can be misleading when applied directly to GA4. Check GA4’s current definitions rather than transferring old assumptions about bounce rate or sessions. For a new implementation, learning current setup and validating success events matters more than reconstructing the old interface.

Choose your next step

Use the setup guide if GA4 is not installed, the reporting guide if data is already arriving, and the key-event guide if business outcomes are unclear. The pageview and conversion-rate guides explain the units behind common reports.