๐ IP Subnet / CIDR Calculator
Enter an IPv4 address with a CIDR prefix (e.g. 192.168.1.10/24) to instantly calculate the subnet mask, network and broadcast addresses, first and last usable host, and total/usable address counts. Handy for network design, subnetting practice, and troubleshooting.
How to use
- Enter an IPv4 address in CIDR notation (e.g. 192.168.1.10/24) in the "IP Address / Prefix" field.
- The subnet mask, network address, and broadcast address are calculated automatically.
- Check the usable host range and total address count.
FAQ
What format should I enter?
Enter an IPv4 address followed by a slash and prefix length, e.g. 192.168.1.10/24. If you omit the prefix, /24 is assumed.
Why do /31 and /32 show 0 usable hosts?
A /32 identifies a single address with no room for network/broadcast addresses, and a /31 (per RFC 3021) is a special two-address point-to-point case โ neither has the usual usable-host range.
How is this used in network design?
Work out the prefix length you need from the required host count, then check the network address, broadcast address, and usable host range that prefix actually gives you.
Is this useful for learning subnetting?
Yes โ try different prefix lengths and watch how the subnet mask and usable host count change, which builds intuition for subnetting.
Is my IP address sent to a server?
No, all calculation happens in your browser and nothing is sent externally.