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Subnet Calculator

Enter an IPv4 address and CIDR prefix to instantly calculate the network address, broadcast address, usable host range, subnet mask and total hosts.

The Subnet Calculator is a free online tool. Enter an IPv4 address and a CIDR prefix (such as 192.168.1.10/24) and it works out the network address, broadcast address, first and last usable host, subnet mask, wildcard mask and the number of usable addresses.
Subnet Calculator

How to use

1

What CIDR notation means

CIDR (Classless Inter-Domain Routing) writes a network as an IP plus a prefix length, like 192.168.1.0/24. The /24 means the first 24 bits identify the network, leaving 8 bits for hosts.

2

Network vs broadcast vs hosts

The network address is the first address in the block, the broadcast is the last, and everything in between is usable for devices. A /24 has 256 total addresses and 254 usable hosts.

3

The subnet mask

The prefix length maps to a dotted mask: /24 is 255.255.255.0, /16 is 255.255.0.0. The wildcard mask is its inverse and is used in access control lists on Cisco devices.

💡 Did you know?

CIDR was introduced in 1993 to slow the exhaustion of IPv4 addresses by replacing the rigid Class A/B/C system with flexible prefix lengths — it extended the usable life of IPv4 by decades.

Reviewed for 2026. Built by a UK-based qualified primary teacher and FA Level 2 coach as part of 247QuickTools' free utility-tools project.