The key metric to evaluate the effectiveness of a conversion (often sales) effort, reflecting the percentage of people converted into buyers (or subscribers, or whatever action is desired) out of the total population exposed to the conversion effort. For websites, the conversion rate is the number of visitors who took the desired action divided by the total number of visitors in a given time period (typically, per month). For email marketing, the conversion rate is the number of people who take an action divided by the total number of people who received the email. (Multiply these numbers by 100 to express the results as percentages.)