Use the following table as a guide to define the number of bits in a Subnet mask.
Subnet mask | Number of bits |
255.255.255.252 | 30 |
255.255.255.248 | 29 |
255.255.255.240 | 28 |
255.255.255.224 | 27 |
255.255.255.192 | 26 |
255.255.255.128 | 25 |
255.255.255.0 | 24 |
255.255.254.0 | 23 |
255.255.252.0 | 22 |
255.255.248.0 | 21 |
255.255.240.0 | 20 |
255.255.224.0 | 19 |
255.255.192.0 | 18 |
255.255.128.0 | 17 |
255.255.0.0 | 16 |