Prefix, subnet mask, wildcard mask and host counts for every IPv4 prefix length.
Prefix
Subnet mask
Wildcard mask
Addresses
Usable hosts
/0
0.0.0.0
255.255.255.255
4,294,967,296
4,294,967,294
/1
128.0.0.0
127.255.255.255
2,147,483,648
2,147,483,646
/2
192.0.0.0
63.255.255.255
1,073,741,824
1,073,741,822
/3
224.0.0.0
31.255.255.255
536,870,912
536,870,910
/4
240.0.0.0
15.255.255.255
268,435,456
268,435,454
/5
248.0.0.0
7.255.255.255
134,217,728
134,217,726
/6
252.0.0.0
3.255.255.255
67,108,864
67,108,862
/7
254.0.0.0
1.255.255.255
33,554,432
33,554,430
/8
255.0.0.0
0.255.255.255
16,777,216
16,777,214
/9
255.128.0.0
0.127.255.255
8,388,608
8,388,606
/10
255.192.0.0
0.63.255.255
4,194,304
4,194,302
/11
255.224.0.0
0.31.255.255
2,097,152
2,097,150
/12
255.240.0.0
0.15.255.255
1,048,576
1,048,574
/13
255.248.0.0
0.7.255.255
524,288
524,286
/14
255.252.0.0
0.3.255.255
262,144
262,142
/15
255.254.0.0
0.1.255.255
131,072
131,070
/16
255.255.0.0
0.0.255.255
65,536
65,534
/17
255.255.128.0
0.0.127.255
32,768
32,766
/18
255.255.192.0
0.0.63.255
16,384
16,382
/19
255.255.224.0
0.0.31.255
8,192
8,190
/20
255.255.240.0
0.0.15.255
4,096
4,094
/21
255.255.248.0
0.0.7.255
2,048
2,046
/22
255.255.252.0
0.0.3.255
1,024
1,022
/23
255.255.254.0
0.0.1.255
512
510
/24
255.255.255.0
0.0.0.255
256
254
/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 read the table
The prefix is the number of fixed bits. Each step down in the table doubles the number of addresses. Usable hosts are the addresses minus two (the network and broadcast addresses), except for /31 (2 hosts, RFC 3021) and /32 (one host). The wildcard mask is the subnet mask turned upside down, used by some router commands.
Numbers worth memorising
/24 is 256 addresses and 254 hosts. Every bit you add halves the block: /25 has 128, /26 has 64, /27 has 32, /28 has 16, /29 has 8 and /30 has 4. Going the other way, /23 is two /24 blocks and /16 is 256 of them. The table was generated with Python's ipaddress module. Use the mask converter for a single prefix, or the hosts guide for the formula.
This is an independent guide. It is not connected with IANA, the IETF or any network equipment maker. Address and port data come from the IANA registries as fetched on 14 November 2026; RFC texts were read from rfc-editor.org. Check the originals for anything you rely on.
Subnet and Ports