CIDR / Subnet Calculator
Enter an address in CIDR notation to calculate the network address, broadcast address, subnet mask, and usable host range.
Frequently asked questions
Why does a /24 have 254 usable hosts instead of 256?+
The first address in the range is reserved as the network address and the last as the broadcast address, neither of which can be assigned to an actual device, leaving 254 usable out of 256 total.
What does the prefix length (the /24 part) actually mean?+
It's how many bits, from the left, are fixed as the network portion of the address. A /24 fixes the first 24 bits (three octets), leaving the last 8 bits (256 addresses) for hosts.
What happens with a /31 or /32?+
A /32 is a single host address with no usable range at all (used for routes to one specific device). A /31 is a special case, defined by RFC 3021, that allows both addresses to be used as a point-to-point link with no separate network/broadcast address.