A quick reference guide for IPv4 CIDR notation.
RIPE’s printable sheet linked at the bottom.
| IP Addresses | Host bits | CIDR Prefix | Subnet Mask |
|---|---|---|---|
| 1 | 0 | /32 | 255.255.255.255 |
| 2 | 1 | /31 | 255.255.255.254 |
| 4 | 2 | /30 | 255.255.255.252 |
| 8 | 3 | /29 | 255.255.255.248 |
| 16 | 4 | /28 | 255.255.255.240 |
| 32 | 5 | /27 | 255.255.255.224 |
| 64 | 6 | /26 | 255.255.255.192 |
| 128 | 7 | /25 | 255.255.255.128 |
| 256 | 8 | /24 | 255.255.255.0 |
| 512 | 9 | /23 | 255.255.254.0 |
| 1,024 | 10 | /22 | 255.255.252.0 |
| 2,048 | 11 | /21 | 255.255.248.0 |
| 4,096 | 12 | /20 | 255.255.240.0 |
| 8,192 | 13 | /19 | 255.255.224.0 |
| 16,384 | 14 | /18 | 255.255.192.0 |
| 32,768 | 15 | /17 | 255.255.128.0 |
| 65,536 | 16 | /16 | 255.255.0.0 |
| 131,072 | 17 | /15 | 255.254.0.0 |
| 262,144 | 18 | /14 | 255.252.0.0 |
| 524,288 | 19 | /13 | 255.248.0.0 |
| 1,048,576 | 20 | /12 | 255.240.0.0 |
| 2,097,152 | 21 | /11 | 255.224.0.0 |
| 4,194,304 | 22 | /10 | 255.192.0.0 |
| 8,388,608 | 23 | /9 | 255.128.0.0 |
| 16,777,216 | 24 | /8 | 255.0.0.0 |
| 33,554,432 | 25 | /7 | 254.0.0.0 |
| 67,108,864 | 26 | /6 | 252.0.0.0 |
| 134,217,728 | 27 | /5 | 248.0.0.0 |
| 268,435,456 | 28 | /4 | 240.0.0.0 |
| 536,870,912 | 29 | /3 | 224.0.0.0 |
| 1,073,741,824 | 30 | /2 | 192.0.0.0 |
| 2,147,483,648 | 31 | /1 | 128.0.0.0 |
| 4,294,967,296 | 32 | /0 | 0.0.0.0 |
See Also: https://www.ripe.net/media/documents/IPv4_CIDR_Chart_2015.pdf
