CIDR / Subnet Calculator
Enter an IP address in CIDR notation (like 192.168.1.0/24) to calculate the subnet's network address, broadcast address, and usable host range.
Last updated: September 5, 2026
Frequently asked questions
What does CIDR notation mean, like /24?
The number after the slash is the prefix length - how many leading bits of the 32-bit IP address are fixed as the network portion. /24 means the first 24 bits (the first three octets) identify the network, leaving 8 bits (256 addresses) for hosts.
How do I calculate the number of usable hosts from a prefix?
Usable hosts = 2^(32 − prefix) − 2, subtracting the network address and broadcast address, which can't be assigned to hosts. A /24 network has 2^8 − 2 = 254 usable host addresses.
Why are there no usable hosts for a /31 or /32?
A /32 is a single address with no room for a network/broadcast pair, and a /31 is a special case (defined in RFC 3021) used for point-to-point links where both addresses in the 2-address block are usable as host addresses, since there's no broadcast needed.
What's the subnet mask for a /24 network?
255.255.255.0 - a /24 prefix means the first 24 bits are all 1s (three full octets of 255), leaving the last octet as all 0s for host addresses.
How is this different from the IP Subnet Calculator?
They compute the same results (network address, broadcast address, usable range), but this tool takes input as a single combined CIDR string like "192.168.1.0/24," while the IP Subnet Calculator uses separate fields for the IP address and prefix length.
What subnet mask corresponds to a /29 network?
255.255.255.248 - a /29 prefix uses 29 of the 32 bits for the network, leaving only 3 host bits (8 total addresses, 6 usable), which as a mask is 255.255.255 followed by 248 (11111000 in binary).