Ecommerce conversion rate is the percentage of website sessions or users that result in a purchase. The calculation depends on whether you are using Universal Analytics or Google Analytics 4 (GA4).

Google Analytics version Conversion-rate calculation
Universal Analytics Transactions ÷ sessions × 100
GA4, session-based Sessions with a purchase key event ÷ total sessions × 100
GA4, user-based Users who made at least one purchase ÷ active users × 100

For example, if 25 of 1,000 sessions resulted in a purchase, the session-based ecommerce conversion rate is 2.5%.

How Ecommerce Conversion Rate Works in GA4

GA4 does not use one metric called "Ecommerce Conversion Rate" in the same way Universal Analytics did. Instead, GA4 reports several related metrics:

  • Session key event rate: The percentage of sessions in which a key event occurred.
  • User key event rate: The percentage of users who triggered a key event.
  • Purchaser rate: The percentage of active users who made at least one purchase.
  • Ecommerce purchases: The number of times the purchase event was triggered.

If you mark purchase as a key event, the session key event rate can represent purchase conversion rate when the report is filtered to that event.

What Is the Ecommerce Conversion Rate Formula?

The right formula depends on whether you want to measure converting sessions or purchasing users.

Session-Based Ecommerce Conversion Rate

Sessions with a purchase ÷ total sessions × 100

Example:

25 purchase sessions ÷ 1,000 total sessions × 100 = 2.5%

This measures the percentage of sessions that produced at least one purchase.

User-Based Purchaser Rate

Users who made at least one purchase ÷ total active users × 100

Example:

20 purchasing users ÷ 800 active users × 100 = 2.5%

This measures the percentage of users who purchased during the selected date range. GA4 defines purchaser rate as the percentage of active users who made one or more purchase transactions.

Purchase-Event Rate

You can also calculate:

Ecommerce purchase events ÷ sessions × 100

This is not always the same as a session conversion rate. One customer can trigger multiple purchase events in one session. For most ecommerce reports, sessions with at least one purchase or users with at least one purchase give a clearer view of conversion.

What Is the Difference Between Ecommerce Purchases and Purchasers?

Ecommerce purchases counts purchase events, while purchasers counts unique users who made at least one purchase.

For example:

  • One customer completes two orders in one session.
  • GA4 records two purchase events.
  • GA4 counts one unique purchaser.
  • A session-based conversion rate counts one converting session.

Google describes the purchase event as the event sent when one or more items are purchased. The Ecommerce purchases metric counts how often that event occurred.

This difference matters when repeat orders, subscriptions or multiple transactions are common.

Where to Find Ecommerce Conversion Data in GA4

To analyse purchase conversion in GA4:

  1. Open the relevant GA4 property.
  2. Go to Reports or Explore.
  3. Add Sessions, Active users, Purchasers and Ecommerce purchases as metrics.
  4. Use Session key event rate or User key event rate where appropriate.
  5. Filter to the purchase key event when you need purchase-specific data rather than the rate for all key events.

The GA4 Traffic acquisition report includes Session key event rate, which Google defines as the percentage of sessions in which a user triggered a key event.

You can also compare the rate by:

  • Default channel group
  • Source and medium
  • Campaign
  • Landing page
  • Device category
  • Country
  • New versus returning users
  • Product category

These comparisons can show whether conversion differences come from traffic source, device, audience or product mix.

What Must Be Configured for GA4 to Measure Ecommerce Conversion Rate?

GA4 needs ecommerce events to be implemented correctly. Product views, add-to-cart actions and purchases are not automatically collected for most websites. You must send the recommended ecommerce events from your website, app or ecommerce platform.

At a minimum, a purchase implementation should send:

  • purchase
  • transaction_id
  • value
  • currency
  • items

Google recommends a unique transaction_id because it helps prevent duplicate purchase events. The items array contains product details such as IDs, names, prices and quantities.

A basic purchase event looks like this:

gtag("event", "purchase", {
  transaction_id: "ORDER_12345",
  value: 89.99,
  currency: "USD",
  items: [
    {
      item_id: "SKU_001",
      item_name: "Example Product",
      price: 89.99,
      quantity: 1
    }
  ]
});

After implementation, use DebugView to check that the event fires correctly. Google says ecommerce data can take approximately 24 to 48 hours to appear in standard reports after users begin generating tagged data.

Universal Analytics Versus GA4

Universal Analytics used a metric called Ecommerce Conversion Rate. It was generally calculated as the percentage of sessions that resulted in a transaction:

Transactions ÷ sessions × 100

Universal Analytics has been replaced by GA4. Current reporting uses the purchase event, key event rates and purchaser metrics instead. Google's legacy documentation identifies Universal Analytics ecommerce conversion rate as an ecommerce reporting metric, while current GA4 documentation uses event-based conversion and ecommerce metrics.

Which Ecommerce Conversion Rate Should You Use?

Use the session-based rate to evaluate website and traffic performance. It answers this question:

What percentage of sessions included at least one purchase?

Use the user-based purchaser rate to measure how many individual users became customers during the selected period.

Do not divide raw ecommerce purchase events by sessions without checking whether customers can complete multiple purchases in one session. That calculation may overstate the number of converting sessions.