This table has been adapted from the table located on the inside front cover of Internet Routing Architectures (Halabi, Cisco Press 1997).
| CIDR Prefix length | Dotted Decimal Netmask | Hex Netmask | Inverse Mask | Number of classfull networks | Number of host addresses * |
|---|---|---|---|---|---|
| /1 | 128.0.0.0 | 80 00 00 00 | 127.255.255.255 | 128 As | 2,147,483,646 |
| /2 | 192.0.0.0 | C0 00 00 00 | 63.255.255.255 | 64 As | 1,073,741,822 |
| /3 | 224.0.0.0 | E0 00 00 00 | 31.255.255.255 | 32 As | 536,870,910 |
| /4 | 240.0.0.0 | F0 00 00 00 | 15.255.255.255 | 16 As | 268,435,454 |
| /5 | 248.0.0.0 | F8 00 00 00 | 7.255.255.255 | 8 As | 134,217,726 |
| /6 | 252.0.0.0 | FC 00 00 00 | 3.255.255.255 | 4 As | 67,108,862 |
| /7 | 254.0.0.0 | FE 00 00 00 | 1.255.255.255 | 2 As | 33,554,430 |
| /8 | 255.0.0.0 | FF 00 00 00 | 0.255.255.255 | 1 A or 256 Bs | 16,777,214 |
| /9 | 255.128.0.0 | FF 80 00 00 | 0.127.255.255 | 128 Bs | 8,388,606 |
| /10 | 255.192.0.0 | FF C0 00 00 | 0.63.255.255 | 64 Bs | 4,194,302 |
| /11 | 255.224.0.0 | FF E0 00 00 | 0.31.255.255 | 32 Bs | 2,097,150 |
| /12 | 255.240.0.0 | FF F0 00 00 | 0.15.255.255 | 16 Bs | 1,048,574 |
| /13 | 255.248.0.0 | FF F8 00 00 | 0.7.255.255 | 8 Bs | 524,286 |
| /14 | 255.252.0.0 | FF FC 00 00 | 0.3.255.255 | 4 Bs | 262,142 |
| /15 | 255.254.0.0 | FF FE 00 00 | 0.1.255.255 | 2 Bs | 131,070 |
| /16 | 255.255.0.0 | FF FF 00 00 | 0.0.255.255 | 1 B or 256 Cs | 65,534 |
| /17 | 255.255.128.0 | FF FF 80 00 | 0.0.127.255 | 128 Cs | 32,766 |
| /18 | 255.255.192.0 | FF FF C0 00 | 0.0.63.255 | 64 Cs | 16,382 |
| /19 | 255.255.224.0 | FF FF E0 00 | 0.0.31.255 | 32 Cs | 8,190 |
| /20 | 255.255.240.0 | FF FF F0 00 | 0.0.15.255 | 16 Cs | 4,094 |
| /21 | 255.255.248.0 | FF FF F8 00 | 0.0.7.255 | 8 Cs | 2,046 |
| /22 | 255.255.252.0 | FF FF FC 00 | 0.0.3.255 | 4 Cs | 1,022 |
| /23 | 255.255.254.0 | FF FF FE 00 | 0.0.1.255 | 2 Cs | 510 |
| /24 | 255.255.255.0 | FF FF FF 00 | 0.0.0.255 | 1 C | 254 |
| /25 | 255.255.255.128 | FF FF FF 80 | 0.0.0.127 | 1/2 C | 126 |
| /26 | 255.255.255.192 | FF FF FF C0 | 0.0.0.63 | 1/4 C | 62 |
| /27 | 255.255.255.224 | FF FF FF E0 | 0.0.0.31 | 1/8 C | 30 |
| /28 | 255.255.255.240 | FF FF FF F0 | 0.0.0.15 | 1/16 C | 14 |
| /29 | 255.255.255.248 | FF FF FF F8 | 0.0.0.7 | 1/32 C | 6 |
| /30 | 255.255.255.252 | FF FF FF FC | 0.0.0.3 | 1/64 C | 2 |
| /31 | 255.255.255.254 | FF FF FF FE | 0.0.0.1 | 1/128 C | 0 |
| /32 | 255.255.255.255 | FF FF FF FF | 0.0.0.0 | 1/256 C | 1 |
* The number of host addresses is the number of available addresses in the given netblock, minus the network number (host = all zeroes) and the broadcast address (host = all ones). A /31 network is useless, and the /32 is typically used to designate a host address (in access lists and the like).