Want to know how many sales a product is generating on Amazon? Here's an easy way, courtesy of AMZSCOUT, a SaaS platform enabling candidate sellers to find a niche and launch their business on Amazon.
They offer a range of free tools, incl. an Amazon sales estimator, right here. The tool is only available for the US market but it will give you a rough idea of the monthly sales per product. You just need to grab the sales rank on a product page. If you can't find the sales rank (sometimes it won't appear), don't worry, there's an easy trick to retrieve a sales rank based on the ASIN (Amazon Standard Identification Number), via this other website.
Here's for instance the sales rank for the Kindle Paperwhite e-reader (ASIN =B00OQVZDJM) in the electronics category in the US: #3.
You can easily find the ASIN in the product URL.
I just pasted 3 in the dedicated field on AMZSCOUT and here's the result. That's $500,000+ worth of sales per month on a single product. Not bad ;-)