What is First User Medium in Google Analytics 4?

Confused by all the "user" vs. "session" metrics in Google Analytics 4? You're not alone. One of the most common points of confusion is the "First user medium" dimension, but understanding it unlocks a much deeper view of how your marketing is actually working. This article will show you exactly what First user medium is, how it differs from other traffic metrics, and how you can use it to make smarter decisions about your content and ad spend.

First, A Quick Refresher on GA4's Measurement Model

To understand 'First user medium,' you first have to grasp the core difference between the old Universal Analytics (UA) and Google Analytics 4. UA was built around the concept of sessions - individual visits to your website. GA4, on the other hand, is built around users and events.

This shift from a session-centric to a user-centric model is fundamental. Instead of just looking at what someone did during a single visit, GA4 tries to show you the entire customer journey over time. This is why you now see all these "First user" dimensions popping up, they are designed to tell you how a user's relationship with your brand started, not just what brought them to your site for their most recent visit.

What Exactly is "First User Medium"? A Simple Definition

First user medium tells you the channel that brought a user to your website or app for the very first time. That's it. It’s the "how" of their initial discovery of your brand.

Think of it like being a regular at your favorite coffee shop. If the barista asks you today, "What brings you in?" you might say, "Oh, I was just walking by." That's your current session's "medium." But if they asked, "How did you originally hear about us?" you might say, "I saw an ad on Instagram a year ago." That’s your "first user medium."

This dimension is sticky. Once Google Analytics assigns a 'First user medium' to a user, it stays with that user's profile for good (or at least, for as long as their tracking cookie/ID persists). Every subsequent visit or conversion will always carry that original acquisition information with it, alongside the data for each new session.

First User Medium vs. Session Medium: The Key Difference Illustrated

The best way to see the difference is with a practical example. Let's follow a customer named Alex on their journey to your website.

Journey of Alex:

• Visit 1: Alex clicks on a paid Facebook ad while scrolling through their feed and lands on your website for the first time.
• Visit 2 (One week later): Alex remembers your brand and searches for it on Google. They click on one of your organic search results.
• Visit 3 (Two weeks later): Alex has your website bookmarked and types the URL directly into their browser to check for new products.

As you can see, the Session medium changes with every visit, telling you how Alex got to your site that specific time. The First user medium remains locked in as 'cpc' because that's what originally introduced Alex to your brand. GA4 logs both, giving you two different lenses to analyze your traffic.

What about the plain "Medium" dimension?

In many standard GA4 reports, like the Traffic Acquisition report, the dimension listed simply as "Medium" is usually referring to the Session medium. The key is to look at the name of the report itself. A report titled "User acquisition" will default to telling you about first touchpoints, while a report titled "Traffic acquisition" will default to telling you about sessions.

Why You Should Care About First User Medium

This isn't just a technical detail, it's a strategic one. Separating acquisition channels from session channels helps you answer critical marketing questions.

1. Discover Your Most Effective "Discovery" Channels

Session medium tells a story about what brings people back, but First user medium tells you what attracts them in the first place. You might find that 'organic' search drives 50% of your total sessions (great for retaining an audience!), but paid social ('cpc') accounts for 60% of your new user acquisition. This insight helps you properly value and fund your top-of-funnel marketing activities that are designed to bring fresh eyes to your brand.

2. Understand the True ROI of Branding Campaigns

Often, awareness-building or branding campaigns don't drive immediate conversions. A user might see your paid ad, not convert, but then come back a week later through organic search to make a purchase. If you only look at session-based reporting with a last-click model, you'd give all the credit to organic search. But by looking at First user medium, you can see that your initial ad spend on 'cpc' was responsible for acquiring that user, giving you a more complete picture of your return on investment.

3. Validate Your Content and SEO Strategy

Is your content successfully attracting people who have never heard of you? Looking at your 'organic' traffic through the First user medium lens gives you the answer. If a top-of-funnel blog post you published is bringing in lots of users whose First user medium is 'organic', you know your SEO and content strategy is working to expand your audience, not just serve your existing one.

Where to Find "First User Medium" in Google Analytics 4

GA4 makes it easy to find this dimension once you know where to look. Here are the two primary places.

1. The User Acquisition Report

This is the main report for analyzing your initial touchpoints. It's practically built around first-user dimensions.

• From the left-hand menu, navigate to Reports > Acquisition > User acquisition.
• By default, this report shows you data by "First user default channel grouping." To see the medium, simply click the small dropdown arrow next to the primary dimension title.
• Select First user medium from the list.

The report will now pivot, showing you key metrics like Users, Engaged sessions, and Conversions, all attributed to the channel that first brought those users to your site.

2. Custom Reports in the "Explore" Section

For more flexible analysis, the Explore tab is where you can build your own reports from scratch.

• Go to the Explore tab from the left-hand menu and click to create a Free form exploration.
• In the Variables panel on the left, click the plus sign (+) next to 'Dimensions'.
• Search for or scroll down to find First user medium. Check the box and click 'Import.' You can also import 'Session medium' here for a side-by-side comparison.
• Next, click the '+' sign next to 'Metrics' and import the numbers you care about, like 'Users,' 'Sessions,' 'Conversions,' and 'Total revenue.'
• Finally, drag First user medium from your 'Variables' panel to the 'Rows' box in the 'Tab Settings' panel. Drag your chosen metrics into the 'Values' box.

This will give you a clean, custom table that lets you see exactly how your original acquisition channels perform against the business metrics you care about most.

Common Questions and Things to Keep in Mind

• What's the difference between "First user source" and "First user medium?" Just like in Universal Analytics, "source" is the specific origin (e.g., 'google', 'facebook.com'), while "medium" is the category of traffic (e.g., 'organic', 'cpc'). Using "First user source / medium" gives you the most granular view (e.g., 'google / cpc').
• Why do I see "(not set)" or "(none)"? This can be caused by a few things, such as missing or broken UTM tags on manual campaigns, privacy restrictions, or tracking discrepancies across different devices. '(direct) / (none)' usually means someone typed your URL directly, used a bookmark, or clicked a non-tagged link from an external application.
• How do deleted cookies affect this? This model is dependent on Google's ability to recognize a user across sessions. If a user deletes their cookies, clears their browser data, or uses a different device where GA4 can't recognize them, they will be treated as a "new" user on their next visit. Their First user medium will be reset to whatever channel brought them back that time.

Final Thoughts

Getting comfortable with GA4’s traffic dimensions is like learning a new vocabulary. First user medium tells you how a customer’s story with your brand began, while Session medium fills in the chapters of their ongoing journey. Using both together gives you the insight needed to build a strategy that not only engages current visitors but effectively acquires new ones.

Analyzing acquisition versus session data can be powerful, but it often requires bouncing between different reports or platforms to see the full picture - like how ad spend on Facebook is influencing first-time user purchases on Shopify. That's why we built Graphed to simplify this process entirely. Instead of configuring complex GA4 reports, we enable you to instantly connect all your marketing data sources and just ask your questions in plain English. For example, you can ask a question like "Create a dashboard comparing my first user medium from Google Analytics against total spend from Facebook Ads for the last quarter," and get a real-time answer visualized instantly. It automates the manual work so you can spend less time digging and more time making smart decisions.