Online Subnet Calculator
The IP Subnet Mask Calculator enables subnet network calculations using network class, IP address, subnet mask, subnet bits, mask bits, maximum required IP subnets and maximum required hosts per subnet.
http://www.subnet-calculator.com/
http://www.subnetmask.info/
http://www.warriorsofthe.net/utils/index.html
http://www.vlsm-calc.net/
