CIDR Subnet Calculator

Use our CIDR subnet calculator below to show information about the subnet that you enter. This calculator for subnetting will be extremely helpful for your CIDR calculations.

CIDR, also known as Classless Inter-Domain Routing replaced what was previously known as Classful Network-Addressing Architecture in 1993 in order to provide a deeper level of networking possibilities and remove the limits the industry was facing.

The CIDR notation consists of an IP address (network address) followed by a separator character (slash, '/'), and the prefix size as a decimal number. The prefix size represents the number of most significant bits in the subnet mask.

When subnetting, the amount of IP addresses in a subnet can be calculated as 2^(32 - prefix size). Generally the number of usable hosts is lower by 2, as the first IP address is used as the network address, and the last is the broadcast address.

There is an exception at times though. This exception is when subnets have a prefix size of 31 and 32. The former is used for point to point links, the latter represents a single host in a network.

Start now with your own CIDR calculation and fill in an IP address then select the number of CIDR mask bits. From there, our CIDR subnet calculator will show you the detailed information about the subnet.

IP address CIDR prefix size