CIDR Calculator

Summary

Enter a CIDR block (e.g. 10.0.0.0/8) to instantly see network address, broadcast, subnet mask, usable host range, and total hosts.

How it works

1. Enter an IPv4 address with a prefix length such as 192.168.1.0/24 in the input field.
2. The tool splits the notation into the host IP and prefix length (0–32).
3. It computes the subnet mask by setting the top N bits of a 32-bit integer.
4. Network address = IP AND mask; Broadcast = IP OR (NOT mask).
5. First usable host = Network + 1; Last usable host = Broadcast - 1.
6. Usable host count = 2^(32 - prefix) - 2 (or 1 for /31, 1 for /32).

Use cases

• Plan IP address allocation for VPCs, data centers, or home networks.
• Verify subnet boundaries before configuring routers or firewalls.
• Calculate the broadcast address needed for ACL or routing rules.
• Determine the number of usable hosts in a proposed subnet.
• Understand supernetting by testing large prefix lengths like /8 or /16.
• Cross-check network documentation and IP scheme designs.
• Teach or learn subnetting concepts interactively.
• Validate CIDR blocks in Terraform, Ansible, or cloud configs.

Frequently Asked Questions