IPv4 Subnet Cheat Sheet
Complete reference table for all CIDR prefix lengths from /0 to /32. Usable hosts assumes standard mode (2 reserved: network + broadcast). For cloud-specific counts, use our subnet calculator.
| CIDR | Subnet Mask | Wildcard | Total Addresses | Usable Hosts | Class |
|---|---|---|---|---|---|
| /0 | 0.0.0.0 | 255.255.255.255 | 4,294,967,296 | 4,294,967,294 | A |
| /1 | 128.0.0.0 | 127.255.255.255 | 2,147,483,648 | 2,147,483,646 | A |
| /2 | 192.0.0.0 | 63.255.255.255 | 1,073,741,824 | 1,073,741,822 | A |
| /3 | 224.0.0.0 | 31.255.255.255 | 536,870,912 | 536,870,910 | A |
| /4 | 240.0.0.0 | 15.255.255.255 | 268,435,456 | 268,435,454 | A |
| /5 | 248.0.0.0 | 7.255.255.255 | 134,217,728 | 134,217,726 | A |
| /6 | 252.0.0.0 | 3.255.255.255 | 67,108,864 | 67,108,862 | A |
| /7 | 254.0.0.0 | 1.255.255.255 | 33,554,432 | 33,554,430 | A |
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,216 | 16,777,214 | A |
| /9 | 255.128.0.0 | 0.127.255.255 | 8,388,608 | 8,388,606 | B |
| /10 | 255.192.0.0 | 0.63.255.255 | 4,194,304 | 4,194,302 | B |
| /11 | 255.224.0.0 | 0.31.255.255 | 2,097,152 | 2,097,150 | B |
| /12 | 255.240.0.0 | 0.15.255.255 | 1,048,576 | 1,048,574 | B |
| /13 | 255.248.0.0 | 0.7.255.255 | 524,288 | 524,286 | B |
| /14 | 255.252.0.0 | 0.3.255.255 | 262,144 | 262,142 | B |
| /15 | 255.254.0.0 | 0.1.255.255 | 131,072 | 131,070 | B |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,536 | 65,534 | B |
| /17 | 255.255.128.0 | 0.0.127.255 | 32,768 | 32,766 | C |
| /18 | 255.255.192.0 | 0.0.63.255 | 16,384 | 16,382 | C |
| /19 | 255.255.224.0 | 0.0.31.255 | 8,192 | 8,190 | C |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,096 | 4,094 | C |
| /21 | 255.255.248.0 | 0.0.7.255 | 2,048 | 2,046 | C |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,024 | 1,022 | C |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 | C |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 | C |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 | - |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 | - |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 | - |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 | - |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 | - |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 | - |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 | - |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 | - |
How to Use This Table
Find your CIDR prefix in the leftmost column. Read across to see the subnet mask, wildcard mask (used in ACLs), total addresses, and usable hosts.
Usable hosts = total addresses − 2 (network address + broadcast address). Exceptions: /31 has 2 usable hosts (RFC 3021), and /32 is a single host route.
Cloud providers reserve additional addresses. AWS reserves 5, Azure reserves 5, OCI reserves 3, and GCP reserves 4. Use our calculator with cloud mode enabled for accurate counts.