How to Check Traffic Sources (Source/Medium) in GA4, with Screenshots [2026]

Do you know where the people visiting your website come from?
The source is the measure that tells you where a visitor came from.
To attract more visitors it matters to know where they arrive from: social media, advertising or search engines.
This article explains in detail how to check the source using Google Analytics 4.

Summary
Knowing where visitors come from matters if you want to attract more of them
In GA4 you mainly check the source, the medium and the referring URL (the referring URL needs a custom dimension set on page_referrer)
Open Reports > Acquisition > Traffic acquisition and switch the dimension to Session source or Session medium
To measure particular activity, add parameters to the link UTM（utm_source・utm_medium・utm_campaign）and build it with Campaign URL Builder
These settings make the effect of each path visible and help you improve

1. What to look at when checking the source in GA4

When checking where visitors come from in Google Analytics 4, you mainly look at the following.

Source
Medium
Referring URL

There are other items you can check, but these are the minimum worth looking at.

Source

The site the visitor came from, such as Google or Yahoo.
The values normally shown as the source are these.

direct	Traffic whose source cannot be identified
google	Traffic from Google
yahoo	Traffic from Yahoo!
bing	Traffic from Bing
notset	A value meaning that, for some reason, Google Analytics could not obtain the data for that item
xxx.com	A specific site, such as instagram.com or facebook.com

Medium

How the source is classified.
The values normally shown as the medium are these.

none	Traffic whose source cannot be identified
referral	A link on a website
oraganic	Direct
notset	A value meaning that, for some reason, Google Analytics could not obtain the data for that item

Referring URL

The particular page URL within the referring site.

2. How to check the source in Google Analytics 4

How to check source and medium

1. Open Google Analytics 4 and, from the left menu, click Reports > Acquisition > Traffic acquisition.
2. Change the dimension. Click where it says Session default channel group at the top of the table.
3. Choosing Session medium shows the medium by session.
4. Choosing Session source shows the source by session.

How to check the referring URL

There is no built-in way to see the referring URL. To see it you need to set a custom dimension in GA4, and it takes a few days after setting it before the data appears. Setting a custom dimension also requires edit rights on the GA4 property.

What is a custom dimension?
A custom dimension is a GA4 feature that lets you add an analysis axis of your own.
GA4 provides a number of default dimensions.
Where those are not enough and you want an axis of your own, a custom dimension is the way to do it.

How to create a custom dimension
1. From the left menu in Google Analytics 4, choose Admin > Custom definitions.
2. Choose Create custom dimension.
3. Set any name you like as the Dimension name. Here we have used Referring URL.
4. Set the Scope to Event.
5. Under Description, briefly explain the dimension you are creating. This is not required.
6. For Event parameter, choose page_referrer.
7. Click Save.

How to check the referring URL
1. From the left menu in Google Analytics 4, choose Reports > Engagement > Events.
2. In the event name column of the table, click session_start.
3. Scroll to the foot of the page and the referring URL is shown.

3. How to measure traffic from a particular source or medium

GA4 lets you measure traffic from a source or medium you specify yourself.
To do that you use UTM parameters.

A UTM parameter works rather like an ID that identifies where traffic came from.

If you want to measure traffic from a newsletter, or from Instagram advertising, you cannot measure it properly without UTM parameters.

How to set UTM parameters

Adding UTM parameters to the link lets you customise and measure the source and medium.

When using UTM parameters, use Campaign URL Builder.
https://ga-dev-tools.web.app/campaign-url-builder/

There are two steps.

1. Open Campaign URL Builder (https://ga-dev-tools.web.app/campaign-url-builder/)
2. Enter the URL, utm_source, utm_medium and utm_campaign
(utm_source and utm_medium are required)

All you do is add three parameters to the link URL: utm_source, utm_medium and utm_campaign. Other parameters are available, but these three are the ones mainly used.
Because the parameters are added to the link itself, this method only works where you can edit the page, email or post the link sits in, such as your newsletter or your own site.

4. In closing

We hope that was useful.
This article has explained how to check where a site’s traffic comes from using GA4.
In strengthening acquisition, it is very important to know where traffic arrives from, and whether the people arriving from a given source go on to sign up.
Do put the analysis of where your traffic comes from to work in attracting more visitors.

The article below explains conversion settings in GA4, which measure a website’s goals such as enquiries from customers, in detail. Do read it alongside this one.
Related article:
[GA4] What are conversion settings? A clear guide to setting them up