GA4 conversion rate tells you what proportion of visits result in a purchase, but the number changes depending on whether you measure sessions or users. For day-to-day ecommerce reporting, session conversion rate is usually the clearest measure because it answers a simple question: out of all the shopping sessions, how many produced an order?

Before calculating anything, confirm that the purchase event is working, revenue is reaching GA4 and internal traffic is excluded. A clean formula cannot repair broken tracking.

Use the GA4 metric that matches the question

1. Confirm purchase is collected. Open Reports > Engagement > Events and find purchase. Then compare the event count and total revenue with Shopify for the same date range, store timezone and market. If purchase is missing or duplicated, fix tracking before calculating a rate.
2. Open the session-based acquisition report. Go to Reports > Acquisition > Traffic acquisition. Set the date range, then use Session default channel group for a channel view or Session source / medium for more detail.
3. Add the correct rate. Click the pencil icon if you have Editor access, choose Metrics, add Session key event rate and save the report. If the report is shared, save it as a new report rather than overwriting a team view.
4. Filter the rate to purchase. Session key event rate includes any event marked as a key event unless the report or exploration is restricted. Build an Exploration with event_name exactly matches purchase, or create a purchase-specific key event where appropriate, so newsletter sign-ups and other actions do not inflate ecommerce conversion.
5. Use the right definition. GA4 session key event rate is the percentage of sessions in which the chosen key event happened at least once. It is not simply total purchase events divided by sessions, because one session can contain more than one purchase event.
6. Break it down. Add device category, landing page or session source / medium in an Exploration. Use enough sessions and purchases for the comparison to mean something.

Validate before reporting

For a manual commercial check, divide the number of sessions containing at least one valid purchase by total sessions, then multiply by 100. If you only have order count, state that you are calculating orders per session, because that is not always identical to GA4's session key event rate.

Compare GA4 against Shopify, but expect some difference from consent, blocked scripts, timezone, refunds and orders created outside the tracked storefront. Investigate a sudden gap or a difference large enough to change a decision.

Sources checked

This guide was checked against Google's current Traffic acquisition report guidance and its explanation of the ecommerce purchase journey.