Every visit to your website came from somewhere. A Google search. A link in an email. An ad. A bookmark. That “somewhere” is the traffic source, and knowing your sources is the difference between guessing and knowing what works.
This guide explains the eight sources that cover almost all web traffic and how Google Analytics 4 sorts them. It also covers why two of its buckets confuse everyone, and how to judge which sources deserve more of your time.
Source, medium, and channel
GA4 records three things about where a session came from.
- Source is the site or platform:
google,facebook,newsletter,partner-site.com. - Medium is the type of traffic:
organic,cpc,referral,email,social. - Channel is GA4’s grouping of source and medium into a short list you can read at a glance: Organic Search, Paid Social, Email, and so on.
Search engines and social platforms set source and medium for you. For everything else, you set them with UTM tags on your links. GA4 then applies its default channel rules to turn source and medium into a channel.
You see all of this in Reports, then Acquisition, then Traffic acquisition. Switch the dimension between Session default channel group, Session source, and Session medium.
The eight sources of website traffic
1. Organic search
A person searched on Google, Bing, or another engine and clicked a normal, unpaid result. GA4 channel: Organic Search.
This is the largest source for most sites and the one SEO exists to grow. It depends on where you rank and on what else is on the results page. A result in position one under an AI Overview gets fewer clicks than the same position on a clean page. If you want to understand the page your visitors are clicking from, start with what a SERP is.
2. Paid search
A person clicked an ad on a search results page. Channel: Paid Search. Source is usually google with medium cpc.
You control volume with budget, and it stops when the budget stops. Google Ads auto-tags its links, so attribution is clean.
3. Direct
GA4 found no referrer. Channel: Direct. Source shows as (direct) and medium as (none).
Direct includes typed URLs and bookmarks, which is what people assume. It also includes clicks from many mobile apps, some email clients, PDFs and documents, and any link that passed through a redirect that dropped the referrer. On many sites Direct is the second-largest channel, and most of it is not people typing your address.
Treat a large Direct number as a measurement gap. Tag your email links and app links with UTM parameters, and Direct shrinks as those visits move to their real channels.
4. Referral
A person clicked a link on another website. Channel: Referral. Source is the linking domain.
Referral traffic is a byproduct of links, mentions, and partnerships. It is often small in volume and strong in engagement, because the visitor arrived with context. Watch this report for spam domains too, as we explain in what is bot traffic.
5. Organic social
A person clicked a link on a social platform without paid promotion. Channel: Organic Social. GA4 recognizes the major platforms by source name.
Social traffic tends to arrive in bursts around posts and to engage less than search or email. That is normal. Judge it on what the visitors do, not on the spike.
6. Paid social
A person clicked a promoted post or ad on a social platform. Channel: Paid Social. Set medium to cpc, paid, or paid_social in your UTM tags so it lands here rather than in Organic Social or Unassigned.
7. Email
A person clicked a link in an email you sent. Channel: Email. Medium must be exactly email (or e-mail, e_mail, e mail) for GA4 to sort it here.
Email is usually the highest-engaging channel a site has, because the visitor already knows you. It is also the channel most often lost to Direct through missing tags.
8. Display and video ads
A person clicked a banner, a native ad, or a video ad. Channels: Display, Paid Video, Cross-network for Google’s automated campaigns. Google Ads tags these for you. Other networks need UTM tags with medium display or cpm.
The two buckets that confuse everyone
Direct we covered. It is the “we do not know” bucket wearing a confident name.
Unassigned is the other one. It appears when a session has a source and medium that match none of GA4’s channel rules. Nearly every time, it is a UTM tag with a medium GA4 does not recognize. For example, medium=newsletter lands in Unassigned, while medium=email lands in Email. Likewise medium=banner lands in Unassigned, while medium=display lands in Display.
The fix is a UTM convention. Pick one spelling for each medium from GA4’s channel list, write it down, and use it everywhere. Google’s help page lists the exact values each channel accepts.
How GA4 assigns a channel
The order matters. For each session GA4 checks, roughly:
- Is it from a Google Ads campaign? Then Paid Search, Paid Shopping, Cross-network, and so on.
- Does the source match a known search engine and the medium look organic? Organic Search.
- Does the source match a known social platform? Organic or Paid Social depending on medium.
- Does the medium say
email? Email. - Is the medium
referral? Referral. - No referrer at all? Direct.
- Nothing matched? Unassigned.
Because of this order, the medium you write in a UTM tag decides the channel. Source names matter less.
Judging a source: sessions are not the score
The Traffic acquisition report sorts by sessions by default. Resist reading it that way. Add these columns and compare sources on them:
| Metric | What it tells you |
|---|---|
| Engagement rate | Share of sessions that lasted 10 seconds, had a conversion, or viewed two pages |
| Average engagement time per session | How long people actually stayed |
| Key events (conversions) | Whether the visitors did the thing you wanted |
| Key events per session | Value per visit, the number that matters for spending decisions |
A source with 40,000 sessions and a 0.1 percent conversion rate is worth less than one with 2,000 sessions and 4 percent. This is also where bot traffic shows itself: a large source with near-zero engagement time is usually not people.
Bounce rate in GA4 is simply the inverse of engagement rate. If you use it, read how to reduce bounce rate first, because it means something different than it did in the old Google Analytics.
Which sources you can change this month
| Source | What moves it | How fast |
|---|---|---|
| Organic search | Rankings, SERP features, content | Months |
| Paid search and social | Budget and targeting | Days |
| List size and send frequency | Days | |
| Referral | Links, mentions, partnerships | Weeks to months |
| Organic social | Posting and audience | Weeks |
| Direct | Better tagging (it shrinks, which is good) | Days |
If you test bought visits as a source, tag them and keep them separate from the channels above so the comparison stays honest. The setup is in how to buy website traffic without wrecking GA4, and the verification steps are in how to check website traffic in GA4.
A five-minute traffic source check
- Open Traffic acquisition and set the date range to the last 90 days.
- Note the share of Direct and Unassigned. Over a third combined means tagging work.
- Add engagement rate, average engagement time, and key events per session.
- Sort by key events per session. That is your real ranking of sources.
- Write down one action for the top source and one for the biggest untagged bucket.
Quick recap
- Traffic sources are where visitors came from. GA4 records source and medium and groups them into channels.
- Eight sources cover almost everything: organic search, paid search, direct, referral, organic social, paid social, email, and display or video.
- Direct is the unknown bucket. Unassigned is the mis-tagged bucket. Both shrink with UTM discipline.
- Compare sources on engagement and conversions per session, not on sessions.
Frequently asked questions
What are the main sources of website traffic?
Organic search, paid search, direct, referral, organic social, paid social, email, and display or video advertising. Google Analytics 4 groups them into default channels using the source and medium of each session. Most sites get the bulk of their visits from organic search and direct.
What is the difference between source, medium, and channel in GA4?
Source is the site or platform the visit came from, like google or facebook. Medium is the type of traffic, like organic, cpc, referral, or email. Channel is GA4's grouping of source and medium pairs into a short list, such as Organic Search or Paid Social. You set source and medium with UTM tags; GA4 derives the channel.
Why is so much of my traffic 'Direct'?
Direct is where GA4 puts any visit with no referrer information. Typed URLs and bookmarks are part of it, but so are clicks from many mobile apps, some email clients, documents, and links that lost their referrer through a redirect. If Direct is more than a third of your traffic, add UTM tags to your emails and app links and watch it shrink.
What does 'Unassigned' mean in GA4?
It means the session had source and medium values that did not match any channel rule. It is almost always a UTM tag with a nonstandard medium, such as 'newsletter' instead of 'email'. Fix the medium to one GA4 recognizes and future sessions sort correctly.
Which traffic source is best?
The one that brings people who do what you want. Compare sources on engagement rate, average engagement time, and conversions per session, not on total sessions. Organic search is usually the largest and most durable. Email and referral often convert best. Paid gives control and speed at a cost.
Sources and further reading
- Google Analytics Help: Default channel group support.google.com
- Google Analytics Help: Traffic acquisition report support.google.com
- Google Analytics Help: Collect campaign data with custom URLs (UTM) support.google.com