If you’ve ever wondered how to properly calculate conversion rate in BigQuery — good news: it’s easier than it sounds. The key is knowing what exactly you want to measure.
In the GA4 interface, it looks polished: pick a goal, see 2.35% conversion rate, and off you go for coffee. But in BigQuery, you’ll need to build it yourself — which also means full flexibility.
So, what is Conversion Rate? At its core, it’s the ratio of sessions (or users) that resulted in a conversion to the total number of sessions (or users). Depending on your goal, you’ll use one of these formulas:
Conversion Rate = Converted Sessions / Total Sessions
or
Conversion Rate = Converted Users / Total Users
How do you calculate it in BigQuery? Let’s say you want to know how many sessions ended with a conversion, like a purchase event. Then:
• Count the total number of sessions
• Count the number of sessions that included a conversion event
• Divide one by the other
That’s it — just a few lines of SQL.
Why go through all this?
• To avoid relying blindly on the GA4 interface
• To build complex, custom funnels
• To plug in your own events, segments, and logic
Takeaway:
The GA4 UI is convenient and user-friendly.
BigQuery is flexible and transparent.
And a truly accurate conversion rate is one you define and control yourself.
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