A conversion rate measures a defined action against a specified base, such as users, sessions, sales leads or eligible advertising interactions. The action might be a purchase, an enquiry, a subscription or a completed application. Its meaning depends on what is counted and what it is divided by.
It is not automatically the percentage of visitors who buy something. A newsletter signup can be a conversion, and an advertising platform can use interactions rather than website visitors as its denominator.
How the calculation works
For a user-based purchase rate, the formula is: users who purchased ÷ total eligible users × 100. If 50 of 1,000 users purchase during a defined reporting period, the rate is 5%.
The successful count goes on top of the fraction. Dividing all users by purchasers would reverse the calculation. The population and period must also match; sales from one audience should not be divided by an unrelated audience’s visits.
Users and sessions give different answers
A user can visit several times. A session is a period of activity, so users and sessions are not interchangeable. Google Analytics provides separate user-based and session-based key-event rates.
Suppose a fictional website has 200 users and 400 sessions in one period. Twenty users purchase, across 30 purchasing sessions. The user purchase rate is 20 ÷ 200 = 10%; the session purchase rate is 30 ÷ 400 = 7.5%.
For these rates, a person or session counts once if the chosen action happened. Repeated purchase events within the same session do not turn it into several purchasing sessions. Google’s session key-event definition specifies sessions containing a key event divided by total sessions.
Ad-platform conversion rate can exceed 100%
Google Ads uses conversions divided by eligible ad interactions. Its conversion rate can exceed 100% when several actions or repeated conversions are counted for one interaction.
That is different from a percentage of distinct people who converted, which cannot exceed 100%. The platform’s event-count metric should not be relabelled as a share of unique customers.
A banner click is not necessarily a purchase
Click-through rate, or CTR, is clicks divided by impressions. Fifty clicks from 1,000 ad impressions give a 5% CTR, without establishing that any purchase occurred. A click can be a chosen conversion action in a particular setup, but the action must be stated.
Nor does every banner click automatically earn a publisher money. Payment depends on the arrangement and valid activity; Google AdSense describes clicks that appear without earnings.
Measurement and comparisons have limits
Offline results can sometimes be linked to online activity. Google Ads supports importing offline conversions, such as a sale following an earlier ad click or call. This requires suitable records and matching; it is not automatic tracking of every shop visit.
Attribution settings and lookback windows affect which interaction receives credit. Traffic mix, missing observations, counting rules and small samples can also affect comparisons.
Conversion rate optimisation, or CRO, is work aimed at improving a defined conversion outcome. It does not guarantee an increase. A higher rate alone does not establish higher profit: fewer eligible visits, lower prices or a different audience can change the result.
Currency conversion is a different meaning
For currencies, conversion rate means an exchange rate, rather than a marketing percentage. The Bank of England explains it as one currency’s price in another.
At a hypothetical rate of US$1.25 per £1, £100 converts to US$125 before fees. The reciprocal is £0.80 per US$1. These are illustrative rates, not current market quotations.
Last checked and updated on November 4, 2026 by the MBN editorial team.