Some of the site metrics on Alexa are estimated based on a sample of global web traffic. Others are Certified based on direct measurement of actual site traffic.
Not all websites implement our on-site analytics and publish the results. For these sites, we show estimated metrics based on traffic patterns across the web as a whole. We identify these patterns by measuring the activity of millions of web users throughout the world. We then use data normalization algorithms to correct for any potential biases. Metrics shown on the Site Overview page default to estimated when Certified metrics are not available. The more traffic a site gets, the more data we have to calculate estimated metrics. Estimated global traffic ranks of 100,000+ are subject to large fluctuations and should be considered rough estimates.
Certified metrics are directly measured instead of estimated. The site owner has installed special Alexa Certify Code on their site that allows Alexa to measure their actual traffic. The site owner can then choose to publicly display any of the following Certified metrics on their Site Overview page:
- Global Unique Visitors
- Global Pageviews
- Audience Geography
Certified metrics have a greater level of accuracy, no matter what the site’s ranking. You can learn about how to get Certified here: How do I get my site’s metrics Certified?