Session Source / Medium

Session Source / Medium in Google Analytics 4 (GA4) identifies where a website session originated and how the user arrived at the site. It helps marketers understand which traffic channels and marketing efforts are driving visits.

The Source indicates the specific platform or website that sent the traffic, while the Medium describes the general category of that traffic.

Understanding Source and Medium

  • Source = The specific origin of the traffic
    Examples:
    • google
    • bing
    • facebook
    • newsletter
    • direct
  • Medium = The marketing channel type
    Examples:
    • organic (unpaid search)
    • cpc (paid search)
    • referral (traffic from another website)
    • email
    • none (direct traffic)

For example:

  • google / organic → Traffic from unpaid Google search results
  • google / cpc → Paid Google Ads traffic
  • facebook / paid_social → Paid ads from Facebook
  • newsletter / email → Email marketing traffic

How Session Source / Medium Works

When a user visits a website, GA4 assigns source and medium values based on:

  • Referrer data
  • UTM parameters (utm_source, utm_medium, utm_campaign)
  • Auto-tagging from platforms like Google Ads

These values are assigned at the session level, meaning they describe how that specific visit started.

Why Session Source / Medium Matters

  1. Marketing Performance Analysis
    Identifies which channels drive the most traffic, engagement, and conversions.
  2. Campaign Attribution
    Helps measure the effectiveness of paid campaigns, email marketing, SEO, and referrals.
  3. Budget Allocation
    Supports data-driven decisions about where to increase or reduce marketing spend.
  4. Traffic Quality Evaluation
    Enables comparison of engagement rate, conversion rate, and revenue per channel.

Session vs. User Source

  • Session Source / Medium → Describes how a specific visit began.
  • User Source / Medium → Refers to the original source that first brought the user to the website.

Understanding this distinction is important when analyzing acquisition performance and attribution models.

Summary

Session Source / Medium in GA4 identifies where a session came from and how the user arrived at a website. By analyzing source and medium data, businesses can measure channel performance, optimize marketing strategies, and allocate budgets more effectively based on actual traffic and conversion insights.