Amazon sorts by sales based on the number of sales of each product. Usually, the sales rank is displayed at the bottom of each product page. Amazon's sales rank is updated every hour, so if a product sells a lot in the first few hours, its ranking will rise very quickly.

In addition, Amazon also sorts based on some other factors, including the category to which the product belongs, the price, the number of reviews, etc. These factors will also affect the ranking of the product. Therefore, even if a product has a high sales volume, if its price is too high or the number of reviews is not enough, it may not rank as well as other products.

In short, Amazon's sales rank is ranked according to the number of sales of the product, but it will also be affected by other factors, such as category, price, number of reviews, etc.