Conversion rate is one of the most-watched metrics — and one of the most often miscalculated. It sounds trivial, but the details decide. Here's what it is and how to read it correctly.
What conversion rate is
Conversion rate is the share of visitors who took a desired action — a purchase, sign-up, form submission. It's calculated as conversions divided by a base (visits, sessions or users) times 100%.
What to divide by (and why it matters)
- Conversions / sessions — common in web analytics.
- Conversions / users — a different view, a different number.
- Orders / store visits — the e-commerce view.
What matters is calculating it the same way every time and knowing what you divide by — otherwise you compare the incomparable. The same "conversion for the week" comes out completely differently depending on the chosen base.
Why patchy measurement skews it
Conversion rate rests on two numbers, and measurement can skew both:
- If client-side loses conversions (ad-blockers, ITP), the rate comes out artificially low.
- If conversions double (missing deduplication), it comes out artificially high.
Server-side tracking gives more complete, deduplicated data, so conversion rate reflects reality — see the complete guide.
Relation to CRO
Raising conversion rate is the goal of CRO (conversion rate optimization) — which can't be done without reliable measurement of this metric.
Summary
Conversion rate is the share of visitors who converted — the key is to calculate it consistently and know what you divide by. Patchy or doubled measurement skews it both ways; server-side tracking makes it more accurate.