All 33 IPv4 prefix lengths and the IPv6 sizes you actually deploy, with netmasks, host counts and cloud limits. Pick a prefix for its full breakdown.
| Prefix | Netmask | Wildcard | Addresses | Usable hosts | Size vs /24 |
|---|---|---|---|---|---|
| /0 | 0.0.0.0 | 255.255.255.255 | 4,294,967,296 | 4,294,967,294 | 16,777,216 /24 networks |
| /1 | 128.0.0.0 | 127.255.255.255 | 2,147,483,648 | 2,147,483,646 | 8,388,608 /24 networks |
| /2 | 192.0.0.0 | 63.255.255.255 | 1,073,741,824 | 1,073,741,822 | 4,194,304 /24 networks |
| /3 | 224.0.0.0 | 31.255.255.255 | 536,870,912 | 536,870,910 | 2,097,152 /24 networks |
| /4 | 240.0.0.0 | 15.255.255.255 | 268,435,456 | 268,435,454 | 1,048,576 /24 networks |
| /5 | 248.0.0.0 | 7.255.255.255 | 134,217,728 | 134,217,726 | 524,288 /24 networks |
| /6 | 252.0.0.0 | 3.255.255.255 | 67,108,864 | 67,108,862 | 262,144 /24 networks |
| /7 | 254.0.0.0 | 1.255.255.255 | 33,554,432 | 33,554,430 | 131,072 /24 networks |
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,216 | 16,777,214 | 65,536 /24 networks |
| /9 | 255.128.0.0 | 0.127.255.255 | 8,388,608 | 8,388,606 | 32,768 /24 networks |
| /10 | 255.192.0.0 | 0.63.255.255 | 4,194,304 | 4,194,302 | 16,384 /24 networks |
| /11 | 255.224.0.0 | 0.31.255.255 | 2,097,152 | 2,097,150 | 8,192 /24 networks |
| /12 | 255.240.0.0 | 0.15.255.255 | 1,048,576 | 1,048,574 | 4,096 /24 networks |
| /13 | 255.248.0.0 | 0.7.255.255 | 524,288 | 524,286 | 2,048 /24 networks |
| /14 | 255.252.0.0 | 0.3.255.255 | 262,144 | 262,142 | 1,024 /24 networks |
| /15 | 255.254.0.0 | 0.1.255.255 | 131,072 | 131,070 | 512 /24 networks |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,536 | 65,534 | 256 /24 networks |
| /17 | 255.255.128.0 | 0.0.127.255 | 32,768 | 32,766 | 128 /24 networks |
| /18 | 255.255.192.0 | 0.0.63.255 | 16,384 | 16,382 | 64 /24 networks |
| /19 | 255.255.224.0 | 0.0.31.255 | 8,192 | 8,190 | 32 /24 networks |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,096 | 4,094 | 16 /24 networks |
| /21 | 255.255.248.0 | 0.0.7.255 | 2,048 | 2,046 | 8 /24 networks |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,024 | 1,022 | 4 /24 networks |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 | 2 /24 networks |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 | 1 /24 network |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 | 1/2 of a /24 |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 | 1/4 of a /24 |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 | 1/8 of a /24 |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 | 1/16 of a /24 |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 | 1/32 of a /24 |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 | 1/64 of a /24 |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 | 1/128 of a /24 |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 | 1/256 of a /24 |
| Prefix | Mask | Host bits | Addresses | /64 subnets |
|---|---|---|---|---|
| /32 | ffff:ffff:: | 96 | 79,228,162,514,264,337,593,543,950,336 | 4,294,967,296 |
| /48 | ffff:ffff:ffff:: | 80 | 1,208,925,819,614,629,174,706,176 | 65,536 |
| /56 | ffff:ffff:ffff:ff00:: | 72 | 4,722,366,482,869,645,213,696 | 256 |
| /60 | ffff:ffff:ffff:fff0:: | 68 | 295,147,905,179,352,825,856 | 16 |
| /64 | ffff:ffff:ffff:ffff:: | 64 | 18,446,744,073,709,551,616 | 1 |
| /112 | ffff:ffff:ffff:ffff:ffff:ffff:ffff:0 | 16 | 65,536 | part of one |
| /126 | ffff:ffff:ffff:ffff:ffff:ffff:ffff:fffc | 2 | 4 | part of one |
| /127 | ffff:ffff:ffff:ffff:ffff:ffff:ffff:fffe | 1 | 2 | part of one |
| /128 | ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff | 0 | 1 | part of one |
The number after the slash is the prefix length: how many leading bits of the address identify the network. An IPv4 address has 32 bits, so a /n network leaves 32 - n host bits and holds 2^(32 - n) addresses. Each step down in prefix length doubles the size of the block; each step up halves it.
Usable hosts. In a normal IPv4 subnet the first address is the network address and the last is the broadcast address, so usable hosts are 2^(32 - n) - 2. Two exceptions: a /31 has two usable addresses on point-to-point links (RFC 3021), and a /32 is a single host.
Netmask and wildcard. The netmask has the prefix bits set to 1 (255.255.255.0 for a /24). The wildcard mask is its inverse (0.0.0.255) and is what Cisco ACLs and OSPF network statements expect.
Alignment. A /n block must start on a multiple of its own size. 192.168.1.64/26 is valid; 192.168.1.50/26 is really 192.168.1.0/26 written with a host address, and tools like the subnet calculator normalise it.
100.64.0.0/10 (/10) is shared address space for carrier-grade NAT, not RFC 1918, but is also not routed on the internet.
| Provider | IPv4 subnet sizes | Reserved per subnet |
|---|---|---|
| AWS VPC | /16 to /28 | 5: first four and the last address (network, VPC router, DNS, future use, broadcast) |
| Azure VNet | /2 to /29 | 5: first four and the last address (network, default gateway, two for Azure DNS, broadcast) |
| Google Cloud VPC | /4 to /29 | 4: first two and last two addresses (network, default gateway, second-to-last, broadcast) |
For IPv6, AWS subnets can be /44 to /64 in steps of /4, while Azure and Google Cloud subnets are always a /64.
IPv6 addresses have 128 bits and the host part of a LAN is always 64 bits, so every LAN is a /64. Planning happens above that: a site usually gets a /48 (65,536 LANs) or a /56 (256 LANs), and links between routers use a /127. Prefix lengths that are multiples of 4 line up with hex digits, which keeps addresses readable and reverse DNS zones simple.