Channel Groupings

Channel groupings in GA4 classify traffic sources into categories like Organic Search, Paid Social, Email, and Direct. They are derived — not collected directly — which means the classification logic can produce wrong answers if your UTM parameters are inconsistent or your traffic sources do not match Google’s assumptions.

Understanding how channel groupings work (and where they fail) is essential for accurate acquisition analysis.

How GA4 classifies channels

GA4 applies a priority-ordered ruleset to every session. The first rule that matches determines the channel:

Rule priority	Channel	Conditions
1	Direct	Source = direct AND Medium is unset or not a medium
2	Cross-network	Campaign name contains “cross-network”
3	Paid Shopping	Source matches a shopping site AND Medium is cpc, ppc, or paid
4	Paid Search	Source matches a search engine AND Medium is cpc, ppc, or paid
5	Paid Social	Source matches a social network AND Medium is cpc, ppc, or paid
6	Paid Video	Source matches a video site AND Medium is cpc, ppc, or paid
7	Display	Medium is display, banner, or expandable
8	Paid Other	Medium is cpc, ppc, or paid (not matched above)
9	Organic Shopping	Source matches a shopping site AND Medium is organic
10	Organic Social	Source matches a social network
11	Organic Video	Source matches a video site
12	Organic Search	Source matches a search engine AND Medium is organic
13	Email	Source or Medium contains “email” or “e-mail”
14	Affiliates	Medium is affiliate
15	Referral	Medium is referral
16	Audio	Medium is audio
17	SMS	Source = sms or medium = sms
18	Mobile Push Notifications	Medium ends with “push” or is “mobile”, “notification”
(None)	Unassigned	No rule matched

The “source matches a search engine” rule uses Google’s maintained list of recognized search engines. Sources not on that list are not classified as Organic Search, even if they are search engines.

Why traffic gets misclassified

Missing or inconsistent UTM parameters

If a paid campaign links have no UTM parameters (or have utm_medium=link instead of utm_medium=cpc), GA4 may classify paid traffic as Referral or Direct. Consistent UTM tagging is the most important factor in accurate channel classification.

Standard paid search UTM:

utm_source=google&utm_medium=cpc&utm_campaign=brand_us

If someone tags it as utm_medium=paid_search instead of cpc, it will not match the Paid Search channel rule — it falls to “Paid Other” or “Unassigned.”

Email campaigns without utm_medium=email

Email newsletters tagged with utm_source=newsletter&utm_medium=nl will not match the Email channel rule (which requires medium to contain “email” or “e-mail”). They will be classified as “Referral” or “Unassigned.”

Correct email UTM: utm_source=mailchimp&utm_medium=email&utm_campaign=march_newsletter

Organic social appearing as Referral

If your social media profiles link to your site without UTM parameters, GA4 classifies them using the referrer. Most social networks are on GA4’s “social” source list, so organic social visits usually classify correctly as Organic Social — but some smaller networks may not be recognized and will appear as Referral.

Subdomains appearing as Referral

If cross-domain tracking is not configured, traffic from your own subdomains (e.g., blog.example.com to shop.example.com) appears as Referral from a subdomain. Configure cross-domain tracking in your stream settings.

Custom channel groupings

GA4 allows you to create custom channel groups to override or extend the default classification. This is useful when:

• Your UTM structure uses non-standard medium values
• You want industry-specific channels (e.g., “Podcast Advertising”)
• You need to combine channels for reporting (e.g., all paid channels as “Paid Media”)

Creating a custom channel group

1. Go to Admin → Channel Groups → Create new channel group.

2. Name the channel group.

3. Define channel rules. Each channel has a name and conditions based on source, medium, campaign, or other traffic parameters.

4. Set the priority order — rules are evaluated top to bottom.

5. Save and set as the default channel group if desired.

Custom channel groups appear as an option in the Traffic Acquisition report’s “Session default channel group” dimension. You can switch between the default system group and your custom group.

Caution

Custom channel groups apply from the date you create them forward. They do not restate historical data. Create them early, before you need to compare historical periods.

Fixing common misclassifications

Fix: Email going to Unassigned

If your email platform uses utm_medium=email_newsletter or any variant, add a custom channel rule:

Channel name: Email
Rule: Medium contains "email" OR Medium contains "e-mail" OR Medium contains "newsletter"

Fix: Paid media going to Unassigned due to non-standard medium

If your agency uses utm_medium=paid_social instead of cpc:

Channel name: Paid Social
Rule: (Medium = "paid_social" OR Medium = "cpc" OR Medium = "ppc")
     AND Source matches regex "facebook|instagram|twitter|linkedin|tiktok"

Fix: Partner traffic appearing as Referral

If you have specific partner domains that should be their own channel:

Channel name: Partner Referral
Rule: Source matches regex "partner1\.com|partner2\.com|distributor\.example\.com"

Channel groupings in BigQuery

The default channel grouping in GA4 uses a logic that you can replicate in BigQuery. Here is a simplified version for common channels:

-- Channel classification in BigQuery
WITH traffic_data AS (
  SELECT
    event_date,
    user_pseudo_id,
    (SELECT value.int_value FROM UNNEST(event_params) WHERE key = 'ga_session_id') AS session_id,
    traffic_source.source AS source,
    traffic_source.medium AS medium,
    traffic_source.name AS campaign
  FROM `project.dataset.events_*`
  WHERE event_name = 'session_start'
    AND _TABLE_SUFFIX BETWEEN '20240101' AND '20240131'
)

SELECT
  event_date,
  CASE
    WHEN source = '(direct)' AND (medium = '(none)' OR medium = '(not set)')
      THEN 'Direct'
    WHEN REGEXP_CONTAINS(LOWER(medium), r'email|e-mail|e_mail')
      THEN 'Email'
    WHEN LOWER(medium) IN ('cpc', 'ppc', 'paid')
      AND REGEXP_CONTAINS(LOWER(source), r'google|bing|yahoo|baidu')
      THEN 'Paid Search'
    WHEN LOWER(medium) IN ('cpc', 'ppc', 'paid')
      AND REGEXP_CONTAINS(LOWER(source), r'facebook|instagram|twitter|linkedin|tiktok|pinterest|snapchat')
      THEN 'Paid Social'
    WHEN LOWER(medium) = 'organic'
      AND REGEXP_CONTAINS(LOWER(source), r'google|bing|yahoo|duckduckgo|baidu')
      THEN 'Organic Search'
    WHEN REGEXP_CONTAINS(LOWER(source), r'facebook|instagram|twitter|linkedin|tiktok|pinterest|snapchat')
      THEN 'Organic Social'
    WHEN LOWER(medium) = 'referral'
      THEN 'Referral'
    WHEN LOWER(medium) = 'affiliate'
      THEN 'Affiliates'
    ELSE 'Unassigned'
  END AS channel,
  COUNT(DISTINCT CONCAT(user_pseudo_id, '.', CAST(session_id AS STRING))) AS sessions
FROM traffic_data
GROUP BY event_date, channel
ORDER BY event_date, sessions DESC

See Custom Channel Grouping in BigQuery for a more complete implementation.

Monitoring for misclassification

Run this BigQuery query periodically to identify traffic going to Unassigned:

SELECT
  traffic_source.source AS source,
  traffic_source.medium AS medium,
  COUNT(DISTINCT CONCAT(user_pseudo_id, '.',
    CAST((SELECT value.int_value FROM UNNEST(event_params) WHERE key = 'ga_session_id') AS STRING)
  )) AS sessions
FROM `project.dataset.events_*`
WHERE event_name = 'session_start'
  AND _TABLE_SUFFIX = FORMAT_DATE('%Y%m%d', CURRENT_DATE() - 1)
GROUP BY source, medium
HAVING sessions > 10
ORDER BY sessions DESC

Any source/medium combination with significant volume that should be in a named channel but is not indicates a tagging or classification issue.

AI traffic sources

Traffic from AI chat tools (ChatGPT, Perplexity, Claude, Microsoft Copilot, Google Gemini) increasingly appears in GA4 — usually classified as Referral or, confusingly, sometimes as Organic Search. Creating a dedicated AI channel gives you visibility into this growing traffic source.

Custom channel group for AI traffic

Create a custom channel rule with these conditions:

Channel name: AI Referral
Rule: Source matches regex "chatgpt\.com|chat\.openai\.com|perplexity\.ai|claude\.ai|copilot\.microsoft\.com|gemini\.google\.com"
Priority: Place above Organic Search and Referral rules

Tip

Google AI Overview clicks appear as regular Organic Search in GA4 — there is no referrer or parameter to distinguish them. The custom channel above only catches traffic from standalone AI chat tools, not from Google’s AI features in search results. See Tracking AI Overview & AI Chat Traffic for a complete guide including a GTM-based detection method.

BigQuery classification

Add AI sources to your BigQuery channel classification:

WHEN REGEXP_CONTAINS(LOWER(source), r'chatgpt\.com|chat\.openai\.com|perplexity\.ai|claude\.ai|copilot\.microsoft\.com|gemini\.google\.com')
  THEN 'AI Referral'

Place this rule before the Organic Search and Referral cases in your CASE statement.

Common mistakes

Expecting UTM tags to fix themselves

UTM tagging requires discipline across your entire marketing team. A single campaign with utm_medium=social (instead of cpc for paid social) will misclassify permanently for those sessions. Establish a UTM taxonomy document and audit campaigns regularly.

Not knowing which channels are in GA4’s default lists

GA4’s recognized source lists for search engines, social networks, and video platforms are maintained by Google and update over time. New platforms may not be on the list. Check the GA4 channel definitions documentation and supplement with custom channel rules for any platform not recognized.

Creating custom channels that overlap

If two custom channel rules can match the same session, the first rule wins. Order matters. Put more specific rules (e.g., specific campaigns) above more general rules (e.g., medium = cpc).

Related articles

Custom Channel Grouping in BigQuery Implement and extend channel classification logic in SQL.

Attribution Settings Configure attribution models that determine which channel gets credit for conversions.

Sessions and Attribution How GA4 assigns source/medium to sessions.

Tracking AI Overview & AI Chat Traffic Complete guide to identifying and measuring AI-referred traffic in GA4.