IP Subnet Calculator
Enter an IP address and CIDR prefix to find the network address, broadcast address, subnet mask, and usable host count.
How subnet calculations work
The CIDR prefix (like /24) indicates how many leading bits of the 32-bit IP address are fixed as the network portion, with the rest available for host addresses. The subnet mask is the corresponding pattern of 1s and 0s expressed in dotted-decimal form (like 255.255.255.0 for /24).
The network address is the lowest address in the range (with all host bits set to 0), and the broadcast address is the highest (with all host bits set to 1) — neither can be assigned to an individual device, which is why usable hosts is 2 less than the total addresses in the range.
Frequently asked questions
What does a /24 subnet mean?
A /24 means the first 24 bits of the IP address are the network portion, leaving 8 bits (256 addresses) for hosts — though 2 of those are reserved for the network and broadcast addresses, leaving 254 usable host addresses.
Why are the network and broadcast addresses not usable for hosts?
The network address identifies the subnet itself, and the broadcast address is used to send a message to every device on that subnet simultaneously — neither represents a specific, individually addressable device.
What happens with a /31 or /32 prefix?
A /32 identifies a single specific address with no room for a network/broadcast distinction. A /31 is a special case (defined in RFC 3021) commonly used for point-to-point links, where both addresses in the 2-address range are usable as host addresses rather than reserved.