CIDR Reference /16 to /32 | Masks and Host Counts
A quick reference table showing subnet masks, total addresses, and usable host counts for common IPv4 CIDR prefixes.
CIDR reference table1
| CIDR | Subnet mask | Total addresses | Usable hosts |
|---|---|---|---|
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /17 | 255.255.128.0 | 32,768 | 32,766 |
| /18 | 255.255.192.0 | 16,384 | 16,382 |
| /19 | 255.255.224.0 | 8,192 | 8,190 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /21 | 255.255.248.0 | 2,048 | 2,046 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 512 | 510 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 |
| /32 | 255.255.255.255 | 1 | 1 |
What to focus on2
/24is the common small-LAN size with 254 usable hosts./26and/27are useful when one larger segment needs to be split into smaller pieces./30is the traditional point-to-point size, while/31is used when you want to avoid wasting addresses./32represents a single host or loopback.