Typical IP Netmask tables

Class-C Netmask table - Most Common

Subnet Mask

Usable
Nodes

bits

255.255.255.000
254
 /24
255.255.255.128
126
 /25
255.255.255.192
62
 /26
255.255.255.224
30
 /27
255.255.255.240
14
 /28
255.255.255.248
6
 /29
255.255.255.252
2
 /30
255.255.255.254
none
 /31
255.255.255.255
1
 /32

Supernets of Classical Class-C

Subnet Mask

Addresses

bits

255.255.000.000
65536
 /16
255.255.128.000
32768
 /17
255.255.192.000
16384
 /18
255.255.224.000
8192
 /19
255.255.240.000
4096
 /20
255.255.248.000
2048
 /21
255.255.252.000
1024
 /22
255.255.254.000
512
 /23
255.255.255.000
256
 /24

Thanks to NTB www.planet.net.au/~neale