IP & CIDR Calculator
Calculate subnet ranges from an IP+mask or CIDR notation.
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Frequently asked questions
- What is a CIDR prefix?
- A CIDR prefix (e.g. /24) states how many bits of an IPv4 address are the network portion. It's the compact equivalent of a subnet mask like 255.255.255.0.
- How is the broadcast address calculated?
- The broadcast address is the network address with every host bit set to 1, the last address in the subnet, reserved for broadcasting to all hosts on that network.
- Why are usable hosts 2 less than total addresses?
- The first address in a subnet is the network address and the last is the broadcast address; neither can be assigned to a device, so usable hosts = total addresses - 2 (except for /31 and /32 subnets).
- What is a wildcard mask?
- A wildcard mask is the inverse of a subnet mask, used mainly in Cisco ACLs and OSPF configuration. Where the subnet mask has a 1 bit, the wildcard mask has a 0, and vice versa.
- Does this calculator support IPv6?
- No, this tool covers IPv4 subnetting only. Use the dedicated IPv6 Calculator for IPv6 addressing.
- What's the difference between the IP+mask mode and the CIDR mode?
- Both modes calculate the same subnet information. IP+mask mode takes an address and a dotted-decimal mask (e.g. 255.255.255.0); CIDR mode takes an address with a slash notation prefix (e.g. /24). Use whichever format matches your source material.