CIDR Reference Table
Quick reference for CIDR notation, subnet masks, and host counts. Perfect for network planning and documentation.
CIDR
Netmask
Wildcard
Hosts
Usable
/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
Common Subnets
- /8 - Class A (16.7M hosts)
- /16 - Class B (65K hosts)
- /24 - Class C (254 hosts)
- /30 - Point-to-Point (2 hosts)
- /32 - Host Route (1 host)
RFC 1918 Ranges
- 10.0.0.0/8
- 172.16.0.0/12
- 192.168.0.0/16
- 127.0.0.0/8 (Loopback)
- 169.254.0.0/16 (Link-local)
Special Cases
- /31 - 2 usable (RFC 3021)
- /32 - Single host
- /0 - All addresses
- 224.0.0.0/4 (Multicast)
- 240.0.0.0/4 (Reserved)