Subnet Calculator
Enter an IPv4 address and CIDR prefix to get the network, broadcast, mask, host range and usable hosts.
Calculate IPv4 subnets instantly
The Subnet Calculator takes an IPv4 address and a CIDR prefix and works out everything you need to plan a network: the network and broadcast addresses, subnet mask, wildcard mask, usable host range, and the number of hosts. Enter your details and the full breakdown appears instantly, all computed in your browser.
What is subnetting?
Subnetting divides a larger IP network into smaller, manageable sub-networks. The CIDR prefix (the /24 in 192.168.1.0/24) tells you how many bits identify the network versus the hosts. A larger prefix means a smaller subnet with fewer hosts. Getting these numbers right is essential for network design, firewall rules, and avoiding address conflicts.
What the calculator shows
| Output | Meaning |
|---|---|
| Network address | The first address — identifies the subnet |
| Broadcast address | The last address — reaches all hosts |
| Subnet mask | Which bits are network vs host |
| Host range | The usable addresses for devices |
| Usable hosts | How many devices the subnet supports |
How to use it
- Enter an IPv4 address.
- Choose the CIDR prefix (/0 to /32).
- Read the network, broadcast, mask, and host details.
Common prefixes
/24— 256 addresses, 254 usable hosts (a typical home/office LAN)./30— 4 addresses, 2 usable hosts (point-to-point links)./16— 65,536 addresses (a large network)./32— a single host address.
Why network and broadcast aren't usable
In each subnet, the first address (network) identifies the subnet itself and the last (broadcast) is reserved for sending to all hosts. That's why a /24 has 256 total addresses but only 254 usable for devices. The calculator accounts for this automatically, so the "usable hosts" figure is always the real number you can assign.
Private and free
All calculations run in your browser — nothing is uploaded. The tool is completely free with no sign-up.
Frequently asked questions
What does the CIDR prefix mean?
It's the number of network bits. /24 means the first 24 bits are the network, leaving 8 bits (254 usable hosts) for devices.
Why are there 2 fewer usable hosts?
The network address and broadcast address in each subnet are reserved, so they can't be assigned to devices.
How many hosts does a /24 have?
256 total addresses and 254 usable hosts.
Is it free?
Yes, completely free with no sign-up, running entirely in your browser.