How to Check Traffic Sources in GA4 | Reading Source/Medium Explained

"Why did traffic to my site increase?" "Where did the users who converted come from?" To improve your site, understanding where users come from is essential. However, because GA4 (Google Analytics 4) has a very different screen layout from the old Universal Analytics (UA), many people get lost trying to figure out where to look to see the traffic source. This article explains the basic steps for checking traffic sources (source/medium) in GA4 and how to read the relevant terms, aimed at beginners.

Key Items That Represent Traffic Sources in GA4

When viewing traffic sources in GA4, three terms come up: "channel," "source," and "medium." Understanding the difference between them first makes the reports far easier to read.

Channel (Default Channel Group)

A channel is a group of traffic sources classified based on a set of rules. It's convenient when you want to view things grouped by broad source, such as "Organic Search," "Paid Search," "Organic Social," or "Direct." In GA4's standard reports, this channel is used as the default display item.

Source

The source refers to the domain of the site where the user was located just before arriving at your site. Search engines like "google" or "yahoo," or specific site domains like "x.com," are displayed. You can grasp the specific origin—"which search engine" or "which social platform."

Medium

The medium indicates the "trigger" or method of the traffic. Values such as "organic" (organic search), "cpc" (cost-per-click advertising), "referral" (links from other sites), or "email" go here. By viewing the combination of source and medium as "source/medium (e.g., google/organic)," you can grasp the traffic source in the most detail.

How to Check Traffic Sources in GA4

The simplest method is to use GA4's standard reports. The following steps get you to "source/medium."

1. Select "Reports" from the left menu
2. Select "Acquisition" → "Traffic acquisition"
3. By default, "Session default channel group" is displayed, so click the "▼" next to the column heading
4. Choose "Session source/medium" from the menu
5. The display switches to "source/medium," and you can check the data for each traffic source

From the same dropdown menu, you can also display only "Session source" or only "Session medium" individually. Use them according to your purpose.

When You Want to See the Referrer URL

If you want to grasp not just the site type or domain of the traffic source but specifically which URL it came from, check the "referrer URL." This is useful when you want to find out which page of an external site has a link to your site. You can check it by adding the "referrer URL" dimension in an Exploration report.

Points to Watch When Viewing Traffic Sources

Measurement Gaps from Unset UTM Parameters

Traffic from email newsletters or apps such as LINE and Instagram may, as-is, lose its source and be classified as "(direct) / (none)" (direct traffic). To measure this correctly, you need to add UTM parameters (utm_source, utm_medium, etc.) to the link URL in advance. In particular, utm_source and utm_medium are required—if either is missing, the parameters become invalid, so be careful.

Your Own Site May Appear as a Source

When there are movements across sites, such as transitions to a payment page, your own domain may be displayed as a source even though it is actually the same site. In this case, configuring "unwanted referrals" (referral exclusion) allows you to measure the correct traffic source.

Summary

To check traffic sources in GA4, the basic approach is to open "Reports" → "Acquisition" → "Traffic acquisition" and switch the dimension to "source/medium." If you keep in mind the flow of grasping the overall picture with channels and then drilling down into specific traffic sources with source/medium, your analysis will go smoothly. However, there are cases where correct data cannot be obtained due to unset UTM parameters or mistakes in referral exclusion, so it's reassuring to review your measurement settings as well. Let's accurately identify traffic sources and use them to improve your website.