Question:
How are Alexa's traffic rankings determined?
Common Questions

Alexa's traffic rankings are based on the usage patterns of Alexa Toolbar users over a rolling 3 month period. A site's ranking is based on a combined measure of reach and pageviews. Reach is determined by the number of unique Alexa users who visit a site on a given day. Pageviews are the total number of Alexa user URL requests for a site. However, multiple requests for the same URL on the same day by the same user are counted as a single pageview. The site with the highest combination of users and pageviews is ranked #1.

Alexa's traffic rankings are for top level domains only (e.g. domain.com). We do not provide seperate rankings for subpages within a domain (e.g. www.domain.com/subpage.html) or subdomains (e.g. subdomain.domain.com) unless we are able to automatically identify them as personal home pages, like those hosted on Geocities and Tripod. If a site is identified as a personal home page, its traffic ranking will have an asterisk (*) next to it: Personal Page Avg. Traffic Rank: 3,456*. Personal pages are ranked on the same scale as a regular domain, so a personal page ranked 3,456* is the 3,456th most popular page among Alexa users.

About the Alexa Traffic Rankings

A listing of all sites on the Web, sorted by traffic...

Alexa computes traffic rankings by analyzing the Web usage of millions of Alexa Toolbar users. The information is sorted, sifted, anonymized, counted, and computed, until, finally, we get the traffic rankings shown in the Alexa service. The process is relatively complex, but if you have a need to know, please read on.

What is Traffic Rank?
The traffic rank is based on three months of aggregated historical traffic data from millions of Alexa Toolbar users and is a combined measure of page views and users (reach). As a first step, Alexa computes the reach and number of page views for all sites on the Web on a daily basis. The main Alexa traffic rank is based on the geometric mean of these two quantities averaged over time (so that the rank of a site reflects both the number of users who visit that site as well as the number of pages on the site viewed by those users). The three-month change is determined by comparing the site's current rank with its rank from three months ago. For example, on July 1, the three-month change would show the difference between the rank based on traffic during the first quarter of the year and the rank based on traffic during the second quarter.

What are sites and Web hosts?
Traffic is computed for sites, which are typically defined at the domain level. For example, the Web hosts www.msn.com, carpoint.msn.com and slate.msn.com are all treated as part of the same site, because they all reside on the same domain, msn.com. An exception is personal home pages, which are treated separately if they can be automatically identified as such from the URLs in question. Also, sites which are found to be serving the "same" content are generally counted together as the same site.

What is Reach?
Reach measures the number of users. Reach is typically expressed as the percentage of all Internet users who visit a given site. So, for example, if a site like yahoo.com has a reach of 28%, this means that if you took random samples of one million Internet users, you would on average find that 280,000 of them visit yahoo.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 measure the number of pages viewed by Alexa Toolbar users. Multiple page views of the same page made by the same user 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 yahoo.com has 70,000 page views per million, this means that 7% of all page views go to yahoo.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).

Some Important Disclaimers

The traffic data are based on the set of Alexa users, which may not be a representative sample of the global Internet population. Known biases include (but are likely not limited to) the following:

* Our users are disproportionately likely to visit alexa.com, amazon.com and archive.org, and traffic to these sites may be substantially overcounted.
* In some cases traffic data may also be adversely affected by our "site" definitions. With tens of millions of hosts on the Internet, our automated procedures for determining which hosts are serving the "same" content may be incorrect and/or out-of-date. Similarly, the determinations of domains and home pages may not always be accurate. When these determinations change (as they do periodically), there may be sudden artificial changes in the Alexa traffic rankings for some sites as a consequence.


In addition to the biases above, the Alexa user base is only a sample of the Internet population, and sites with relatively low traffic will not be accurately ranked by Alexa due to the statistical limitations of the sample. Alexa's data come from a large sample of several million Alexa Toolbar users; however, this is not large enough to accurately determine the rankings of sites with fewer than roughly 1,000 total monthly visitors. Generally, Traffic Rankings of 100,000+ should be regarded as not reliable because the amount of data we receive is not statistically significant. Conversely, the more traffic a site receives (the closer it gets to the number 1 position), the more reliable its Traffic Ranking becomes.