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CIDR Calculator

Use the CIDR calculator to convert an IP address and prefix into the network range, subnet mask, and usable host count.

⌘ Runs in browser ◴ No data stored ⌁ Free

Concept

CIDR calculation for network policy validation

Use the CIDR calculator to derive precise network boundaries from an IP and prefix, then validate subnet plans and security policies before applying any traffic-control rule.

Before adding firewall, routing, or cloud security group rules, check the network and broadcast addresses first to avoid exposing more addresses than intended.

Review the minimum and maximum host addresses and usable host count together to align subnet capacity and access scope with the environment policy.

Subnet design review

Validate each CIDR block before splitting or aggregating networks and detect overlap that can break routing or create ambiguous policy scope.

Firewall and SG validation

Use the calculated boundaries to tighten ingress and egress allowlists in firewall rules, security groups, and NACLs.

Pre-apply checkpoint

Before applying routing changes or ACL updates, re-check network/broadcast boundaries and host ranges against existing policy documents.

The result is an operational aid for design checks. Before production routing, firewall, or security-group rollout, verify current policy, route tables, and ACL standards as a final step.

IPv4 CIDR or range input
CIDR calculation result

How to use

  1. 1 Enter an IP address with a CIDR prefix length.
  2. 2 Calculate the network address, broadcast address, subnet mask, and host range.
  3. 3 Choose a target prefix in subnet slicing to review the child CIDR list.
  4. 4 Copy the CIDR list or CSV for firewall, routing, or security group configuration.

Common use cases

  • CIDR calculator for 10.0.0.0/16
  • Slice 10.2.0.0/15 into /20 subnets
  • IP address to CIDR range check
  • Subnet mask and usable host calculation

Frequently asked questions

What input formats does the CIDR calculator support?

It supports IPv4 CIDR such as 192.168.1.0/24, IP + subnet mask such as 192.168.1.1 255.255.255.0, IP ranges such as 192.168.1.10 - 192.168.1.20, and mask-only inputs such as /24 or 255.255.255.0.

What results can I check?

You can view the network address, broadcast address, first and last host, total addresses, usable hosts, subnet mask, wildcard mask, IP class, whether the address is private or reserved, and the child CIDR slicing result.

Can I split a large CIDR into smaller CIDR blocks?

Yes. After calculating a CIDR, choose a split prefix such as /20 or /24 in subnet slicing to view child CIDR blocks, IP ranges, and usable host counts, then copy the list or CSV.

Does it calculate IPv6?

No. The current calculation logic targets IPv4 addresses and prefixes from 0 to 32.

Related workflow

CIDR CalculatorCalculate the network range first for firewall rules or allowlists. → Chmod CalculatorWhen network restrictions go with deployed files, confirm the permission mode as well. → Htpasswd GeneratorIf IP rules are not enough, prepare a server-compatible htpasswd entry for an added auth layer.