It's not 100 million web sites, because Let's Encrypt certificates expire every 90 days, and you have to get a new certificate if you want to add or remove a domain name, and you can get duplicative certificates as long as they're within the rate limits.

As I said in my post at

https://www.eff.org/deeplinks/2017/06/lets-encrypt-has-issue...

it's probably between 17 million and 46 million web sites, although it could be a bit smaller than 17 million at the most restrictive notion of "web site" if you don't consider subdomains to be a separate web site even if they have different content and are operated by a different person.

You can see all of the certificates at

https://crt.sh/?Identity=%25&iCAID=7395 https://crt.sh/?Identity=%25&iCAID=16418

and you can also get a lot of the data from

https://scans.io/

or https://www.censys.io/ (registration required), although the people running it told me in connection with this that their Certificate Transparency data is not as current at the moment as crt.sh's data.