IPv4 Subnet Prefixes /8 to /32
Pick a prefix to see its mask, how many hosts it holds, a worked example and where it is used in real networks. The table is a quick reference; each row links to the full page.
| Prefix | Subnet mask | Wildcard | Block size | Usable hosts |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 | 1 (first) | 16,777,214 |
| /9 | 255.128.0.0 | 0.127.255.255 | 128 (second) | 8,388,606 |
| /10 | 255.192.0.0 | 0.63.255.255 | 64 (second) | 4,194,302 |
| /11 | 255.224.0.0 | 0.31.255.255 | 32 (second) | 2,097,150 |
| /12 | 255.240.0.0 | 0.15.255.255 | 16 (second) | 1,048,574 |
| /13 | 255.248.0.0 | 0.7.255.255 | 8 (second) | 524,286 |
| /14 | 255.252.0.0 | 0.3.255.255 | 4 (second) | 262,142 |
| /15 | 255.254.0.0 | 0.1.255.255 | 2 (second) | 131,070 |
| /16 | 255.255.0.0 | 0.0.255.255 | 1 (second) | 65,534 |
| /17 | 255.255.128.0 | 0.0.127.255 | 128 (third) | 32,766 |
| /18 | 255.255.192.0 | 0.0.63.255 | 64 (third) | 16,382 |
| /19 | 255.255.224.0 | 0.0.31.255 | 32 (third) | 8,190 |
| /20 | 255.255.240.0 | 0.0.15.255 | 16 (third) | 4,094 |
| /21 | 255.255.248.0 | 0.0.7.255 | 8 (third) | 2,046 |
| /22 | 255.255.252.0 | 0.0.3.255 | 4 (third) | 1,022 |
| /23 | 255.255.254.0 | 0.0.1.255 | 2 (third) | 510 |
| /24 | 255.255.255.0 | 0.0.0.255 | 1 (third) | 254 |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 (fourth) | 126 |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 (fourth) | 62 |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 (fourth) | 30 |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 (fourth) | 14 |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 (fourth) | 6 |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 (fourth) | 2 |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 (fourth) | 2 |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 (fourth) | 1 |
How to read the table
Block size is how far apart networks of that size start, counted in the octet where the mask stops being 255. For a /26 the mask ends in 192, so the block size is 256 − 192 = 64 and networks start at .0, .64, .128 and .192. For /8, /16 and /24 the boundary falls between octets, so the block size is 1 in the last full octet.
Usable hosts is 2(32 − prefix) − 2, because the first address is the network and the last is the broadcast. /31 and /32 are exceptions: a /31 has 2 usable addresses on point-to-point links (RFC 3021) and a /32 is a single address. Cloud providers reserve more — see the AWS, Azure and GCP calculators.
Well-known networks
- 10.0.0.0/24 — The First /24 of the 10 Range
- 10.0.0.0/8 — The Largest Private Range
- 100.64.0.0/10 — Carrier-Grade NAT Space
- 127.0.0.0/8 — The Loopback Range
- 169.254.0.0/16 — Link-Local Addresses
- 172.16.0.0/12 — The Middle Private Range
- 172.17.0.0/16 — Docker's Default Bridge
- 192.168.0.0/16 — The Home Network Range
- 192.168.0.0/24 — The Other Default Home Network
- 192.168.1.0/24 — The Most Common Home Network
Calculators
Have a specific address? Use the subnet calculator. Converting masks? Try the subnet mask calculator or the wildcard mask calculator. Planning several subnets of different sizes? Use the VLSM calculator. Learning to do it by hand? Drill it in the subnetting practice trainer and keep the subnet cheat sheet next to you.