According to Alexa’s official website, the rank is calculated by estimating the browsing behavior of people to the sites and the estimated number of page views on the site over the past 3 months. The lower the Alexa score, the better is the visibility. The site with the highest unique visitors and unique pageviews is ranked #1.
Alexa Ranking helps you to compare how your website is doing relative to that of all other competitors on the web. Alexa has a large traffic data panel with millions of people all over the world. It is a complex calculation that estimates the number of visitors to all the sites on the Internet.
Along with that, it involves correcting for biases as well as identifying and gets rid of fake or spam traffic. Moreover, the data scientists of Alexa Ranking put in their best efforts to provide data free of noise. So, you can make appropriate decisions for your website.