Subnet mask cheat sheet
Netmask, address count and usable hosts for every IPv4 prefix length from /8 to /32.
| Prefix | Netmask | Addresses | Usable hosts | AWS usable |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | n/a |
| /9 | 255.128.0.0 | 8,388,608 | 8,388,606 | n/a |
| /10 | 255.192.0.0 | 4,194,304 | 4,194,302 | n/a |
| /11 | 255.224.0.0 | 2,097,152 | 2,097,150 | n/a |
| /12 | 255.240.0.0 | 1,048,576 | 1,048,574 | n/a |
| /13 | 255.248.0.0 | 524,288 | 524,286 | n/a |
| /14 | 255.252.0.0 | 262,144 | 262,142 | n/a |
| /15 | 255.254.0.0 | 131,072 | 131,070 | n/a |
| /16 | 255.255.0.0 | 65,536 | 65,534 | 65,531 |
| /17 | 255.255.128.0 | 32,768 | 32,766 | 32,763 |
| /18 | 255.255.192.0 | 16,384 | 16,382 | 16,379 |
| /19 | 255.255.224.0 | 8,192 | 8,190 | 8,187 |
| /20 | 255.255.240.0 | 4,096 | 4,094 | 4,091 |
| /21 | 255.255.248.0 | 2,048 | 2,046 | 2,043 |
| /22 | 255.255.252.0 | 1,024 | 1,022 | 1,019 |
| /23 | 255.255.254.0 | 512 | 510 | 507 |
| /24 | 255.255.255.0 | 256 | 254 | 251 |
| /25 | 255.255.255.128 | 128 | 126 | 123 |
| /26 | 255.255.255.192 | 64 | 62 | 59 |
| /27 | 255.255.255.224 | 32 | 30 | 27 |
| /28 | 255.255.255.240 | 16 | 14 | 11 |
| /29 | 255.255.255.248 | 8 | 6 | n/a |
| /30 | 255.255.255.252 | 4 | 2 | n/a |
| /31 | 255.255.255.254 | 2 | 2 | n/a |
| /32 | 255.255.255.255 | 1 | 1 | n/a |
Usable hosts leave out the network and broadcast addresses, except for /31 and /32. AWS reserves 5 addresses in every subnet. To check a specific block or split a VPC into subnets, use the CIDR subnet calculator.