This is a very useful subnetting chart that will help out a student of Cisco networking. This shows how many subnets you can have with a certain subnet mask. This can be tricky to learn and something like this will really help out.
Another way to calculate subnetting is with the sipcalc command for Linux. This will calculate all of the subnets for a certain address and subnet mask.
Here is an example.
ubuntu ~/nt $ sipcalc 192.168.0.1/26 -[ipv4 : 192.168.0.1/26] - 0 [CIDR] Host address - 192.168.0.1 Host address (decimal) - 3232235521 Host address (hex) - C0A80001 Network address - 192.168.0.0 Network mask - 255.255.255.192 Network mask (bits) - 26 Network mask (hex) - FFFFFFC0 Broadcast address - 192.168.0.63 Cisco wildcard - 0.0.0.63 Addresses in network - 64 Network range - 192.168.0.0 - 192.168.0.63 Usable range - 192.168.0.1 - 192.168.0.62
This makes subnet calculation very easy indeed.
A lot more information on subnetting and more charts here: http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13790-8.html.
IPv6 subnetting information: http://en.linuxreviews.org/IPv6_subnet_matrix_table.