In most of the situation, if you want to know the ip address of a website, you just ping the website, it will return the ip address. But if the website block ICMP, you may not able to get the ip address.
Here i going to intro one of the good Google Chrome Extension called Website IP which allow you to see the ip address of the website you are currently looking at. IP address of the website will show at the bottom of the web page.
Website with IPv4
Website with IPv6