Subnet Calculator 🔒 Runs locally in your browser — nothing is uploaded.

Work out network, broadcast, mask and host range from CIDR.

Network address
Broadcast address
Subnet mask
Wildcard mask
First host
Last host
Usable hosts
Total addresses
Class

About this tool

Subnetting turns one address block into many smaller networks, and the arithmetic — masks, wildcards, host ranges — is fiddly to do by hand. Enter an IPv4 address with a CIDR prefix like /24, or a dotted netmask, and this calculator lays out the network and broadcast addresses, the subnet and wildcard masks, the first and last usable host, the total and usable host counts and the address class.

It is pure arithmetic computed in your browser — nothing is sent anywhere. Handy for planning a network, configuring a firewall rule or just double-checking a range.

Frequently asked questions

What does the /24 in an IP address mean?

That's CIDR notation — it means the first 24 bits of the address are the network portion and the remaining 8 bits identify hosts within it. A /24 network has 256 total addresses (254 usable, since the first and last are reserved for the network and broadcast address).

What's the difference between the network address and broadcast address?

The network address (the first address in the range) identifies the subnet itself and can't be assigned to a host. The broadcast address (the last address) is used to send a packet to every host on that subnet simultaneously — neither is usable for an individual device.

What does the wildcard mask show?

It's the bitwise inverse of the subnet mask, used in access-control lists and routing configurations (like Cisco ACLs) where you specify which bits to ignore rather than which bits must match.

Is my IP address sent anywhere when I use this calculator?

No. All subnet math runs locally in JavaScript in your browser — nothing about the address you enter is transmitted or logged.

Why does a /31 or /32 network show 0 usable hosts?

With only 1-2 total addresses, there's no room for separate network and broadcast addresses. /31 is a special case used for point-to-point links (both addresses are usable per RFC 3021), and /32 is a single host route — the usable-hosts count here follows the classic reserve-two-addresses rule and doesn't reflect that RFC 3021 exception.