Reach measures the number of users(unique visitors). Reach is typically expressed as the percentage of all Internet users who visit a given site. So, for example, if a site like alexarankingboost.com has a reach of 8%, this means that if you took random samples of one million Internet users, you would on average find that 80,000 of them visit alexarankingboost.com. Alexa expresses reach as number of users per million. Alexa's one-week and three-month average reach are measures of daily reach, averaged over the specified time period. The reach rank is a ranking of all sites based solely on their reach. The three-month changes are determined by comparing a site's current reach and reach rank with its values from three month
ago.
What are Page Views?
Page views are calculated by number of pages viewed by Alexa Toolbar using visitors. Multiple page views of the same page done by the same visitor on the same day are counted only once. The page views per user numbers are the average numbers of unique pages viewed per user per day by the users visiting the site. The page view rank is a ranking of all sites based solely on the total number of page views (not page views per user). The three-month changes are determined by comparing a site's current page view numbers with those from three month ago.Page views per million indicates what fraction of all the page views by toolbar users go to a particular site. For example, if alexarankingboost.com has 30,000 page views per million, this means that 3% of all page views go to alexarankingboost.com.If you summed the fractional page views over all sites, you would get
100% (this is not true of reach, since each user can of course visit more than one site).
How Are Traffic Trend Graphs Calculated?
The daily trafficrank in the Trend graphs allows you to see short term fluctuations in traffic much more clearly. Daily traffic rankings may benefit sites withshort term high traffic, while the three month traffic ranking benefits sites with consistent traffic over a long period of time. Since the consistent traffic is a better indication of a site's value, the three-month traffic rank represents the site's overall rank.