Alexa’s Traffic Ranks are based on the site visitors statistics supplied by way of users in Alexa’s worldwide information panel over a rolling three month duration. … A website’s rating is primarily based on a blended measure of Unique Visitors and Pageviews. Unique Visitors are decided by means of the number of unique Alexa users who go to a website on a given day.
Alexa may be a global ranking system that utilizes internet traffic data to compile a list of the most popular websites, the Alexa Rank. The lower your Alexa rank, the more popular (for example, a web site with the rank of one has the most visitors on the internet).