What this tool calculates
A CIDR block like 192.168.1.0/24 packs a lot of information into a short string. This calculator unpacks it: the network and broadcast addresses that bound the block, the subnet and wildcard masks, the first and last usable host addresses, and the total and usable host counts. It runs entirely in your browser, so nothing you type leaves your machine.
Frequently asked questions
Why are usable hosts two fewer than the total?
The first address in a block is the network address and the last is the broadcast address. Neither can be assigned to a host, so usable hosts are two fewer, except for /31 and /32 blocks which follow special rules.
What does the prefix length mean?
The number after the slash is how many bits are fixed for the network. A smaller number, like /16, means a larger block with more hosts. A larger number, like /28, means a smaller block with fewer hosts.
What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. It marks which bits can vary and is used in tools like access control lists and some routing configurations.