IP Subnet Calculator

What is CIDR?

CIDR notation specifies an IP address and its routing prefix. For example, 192.168.1.0/24 represents a network with 256 addresses.

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Reference Tables

Common Subnet Masks

CIDR Subnet Mask Usable Hosts
/8 255.0.0.0 16,777,214
/12 255.240.0.0 1,048,574
/16 255.255.0.0 65,534
/20 255.255.240.0 4,094
/24 255.255.255.0 254
/25 255.255.255.128 126
/26 255.255.255.192 62
/27 255.255.255.224 30
/28 255.255.255.240 14
/29 255.255.255.248 6
/30 255.255.255.252 2
/31 255.255.255.254 2 (point-to-point)
/32 255.255.255.255 1

Private IP Address Ranges

Class Range CIDR
A 10.0.0.0 - 10.255.255.255 10.0.0.0/8
B 172.16.0.0 - 172.31.255.255 172.16.0.0/12
C 192.168.0.0 - 192.168.255.255 192.168.0.0/16