Conversion
Conversion rate
Also called CVR.
Conversion rate is completions of a goal divided by the chosen denominator. The denominator is a choice, and the choice changes the number.
How it is measured
Take goal events in the period and divide by sessions, visitors, or landing visits. Sessions give a per-visit rate, visitors give a per-person rate. Say which one you used.
Tarsier's goals page divides goal events by visitors in the period, so the rate reads as completions per visitor.
Worked example
A candle shop gets 1,800 visitors in a week and 36 purchases. That is 2.0 percent per visitor. The same week has 2,300 sessions, so per session it is 1.6 percent. A friend's shop says 3 percent, and counts only sessions that reached checkout.
The comparison dissolves once both owners use visitors as the base.
How it differs
Conversion rate is a ratio. A conversion is the numerator. A goal is the definition behind it. A session is the other common denominator.
Common errors
Changing the denominator between reports. Dividing by pageviews. Quoting a rate from a few visitors. Comparing to industry averages. Counting repeat buyers as new.
In practice
Use one denominator, state it on the chart, and ignore rates built from fewer than a few hundred visitors.