CIDR / Subnet Calculator
Enter an IPv4 address with a CIDR prefix (e.g. 192.168.1.10/24) or a subnet mask (e.g. 192.168.1.10/255.255.255.0), and this tool calculates the network address, broadcast address, subnet mask, wildcard mask, and the range and count of usable hosts in real time. Handy for network design and checking subnet splits. Everything happens in your browser, and nothing you type is ever sent to a server. If you need to check file permissions, try the Chmod Permission Calculator as well.
🔒 Runs in your browser · Your data is never sent to a server
| Network address | |
| Broadcast address | |
| Subnet mask | |
| Wildcard mask | |
| First usable host | |
| Last usable host | |
| Usable host count | |
| Total address count |
Notes
- Only IPv4 is supported; IPv6 addresses are not.
- The part after the slash can be either a bit-count prefix ("/24") or a dotted subnet mask ("/255.255.255.0").
- An IP address octet with a leading zero (e.g. "01") is treated as invalid, to avoid any ambiguity with octal interpretation.
- /31 is treated as a point-to-point link (RFC 3021) with both addresses usable, and /32 is treated as a single host with just 1 usable address.
Glossary
CIDR notation (e.g. 192.168.1.0/24)
An IP address followed by a "/" and a prefix length (the number of network bits). "/24" means the first 24 bits are the network part and the remaining 8 bits are the host part.
Subnet mask (e.g. 255.255.255.0)
A dotted-decimal value with the network-part bits set to 1, showing how much of the address is the network. It maps one-to-one to a CIDR prefix length (/24 = 255.255.255.0).
Network address & broadcast address
The network address is the first address in a subnet (all host bits zero) and identifies the network itself — it can't be assigned to a host. The broadcast address is the last one (all host bits one) and is used to send to every host on that subnet at once.
Wildcard mask
The bitwise inverse of a subnet mask, used in place of a subnet mask in access control list (ACL) configuration on Cisco devices, for example.
Usable host count
The number of addresses that can actually be assigned to devices in a subnet. Normally this excludes the network and broadcast addresses, but /31 is treated as a point-to-point link (RFC 3021) with both addresses usable, and /32 is treated as a single host with just 1 usable address.
FAQ
What does the number after the slash (/24, /16) mean?
It is the number of leading bits used for the network portion. /24 means 24 network bits and 8 host bits, giving the subnet mask 255.255.255.0. Smaller numbers describe larger networks.
How is the number of usable hosts calculated?
It is the total number of addresses minus the network and broadcast addresses. For /24 that is 256 − 2 = 254. /31 and /32 are handled as special cases.
Does it support IPv6?
Currently only IPv4 is supported. IPv6 prefix calculations are not available.
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