For those who have to work with IP’s and subnets, I have only one word; Bitcricket IP Calculator.
It converts decimal IP’s into binary or hexadecimal IP’s (and, the other way around too); it gives you the IP class; it calculates subnets, with the number of hosts/subnet, and gives you the number of host bits; and many more!
Shiny tool to quickly do subnet calculations. Has proven it’s use when doing the Cisco CCNA tests. 😉