Subnet / CIDR Calculator
Calculate network address, broadcast address, subnet mask, and usable host range from any IP and CIDR prefix.
The number after the slash tells you how many bits of the 32-bit address are fixed as the "network" part. A smaller number (like /8) means a huge network; a larger one (like /30) means a tiny one.
The first address in the range. It identifies the subnet itself and can't be assigned to a device.
The last address in the range, reserved for sending a message to every device on the subnet at once.
Another way of writing the same CIDR prefix — it marks which bits of an IP are the network part vs. the host part.
Total addresses minus 2 (the network and broadcast addresses, which can't be assigned to devices). A /31 or /32 is a special case used for point-to-point links, so it has 0 "usable" hosts by this definition.
The actual range of IPs you can assign to devices — routers, computers, servers — on this subnet.
About the Subnet / CIDR Calculator
A subnet calculator breaks an IP address and CIDR prefix down into the network address, broadcast address, subnet mask, and usable host range for that network.
Common CIDR prefixes
| Prefix | Total addresses | Usable hosts | |
|---|---|---|---|
| /30 | 4 | 2 | |
| /29 | 8 | 6 | |
| /28 | 16 | 14 | |
| /24 | 256 | 254 | |
| /16 | 65,536 | 65,534 |
How to use
Enter the IP address for your network, such as 192.168.1.0.
Enter the CIDR prefix, the number after the slash, from 0 to 32.
Read off the network address, broadcast address, and usable host range for that subnet.
Worked examples
Example: a common home network
The IP address 192.168.1.0 with a /24 prefix.
A /24 reserves the first and last address in the range for the network and broadcast addresses, leaving 254 addresses that can actually be assigned to devices.
Frequently asked questions
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