CIDR Calculator

Enter a IP Address - Required
Enter CIDR Notation or Subnet Mask - One Required

IP:/ Subnet Mask

What is CIDR?

CIDR is the new addressing scheme which replaces the traditional Class A, B, C scheme with a generalized network prefix. Instead of being limited to network identifiers of 8, 16, or 24 bits, CIDR uses anywhere from 13 to 27 bits. this allows creation of IP blocks which more closely fit an organizations specific needs.

CIDR addresses include the standard 32-bit IP address and also information on how many bits are used for the network prefix. As per my example at the head of this page.

My thanks to Vanessa, whose blog post Basic Fun with IPs in PHP inspired this tool.