CIDR Calculator

Calculate IPv4 and IPv6 prefix boundaries locally without scanning or testing reachability.

Runs in your browser

Runs in this browser. Input is not sent to a utility provider.

Input limits

  • One IPv4 or IPv6 prefix up to 256 characters.

Calculate an address prefix

Enter one IPv4 or IPv6 address with a prefix. Calculation uses integer arithmetic in this browser and never enumerates the range.

Use one address followed by / and a decimal prefix length. IPv4 accepts /0 through /32; IPv6 accepts /0 through /128. Zone identifiers are not supported. Limit: 256 characters.

CIDR calculation

Example tasks
  • Calculate the start, end, mask, wildcard mask, and exact size of an IPv4 prefix.
  • Normalize a compressed, full, or embedded-IPv4 IPv6 prefix and review its exact range.
  • Review the distinct address semantics of IPv4 /31 and /32 or IPv6 /127 and /128.
What this tool does not prove
  • Address math runs locally and does not perform DNS, scan, contact, or test reachability for any address.
  • The classification applies only to the entered address and a finite IANA-derived table reviewed on July 23, 2026. A non-match does not prove global reachability.
  • Registry reachability fields do not guarantee routability in a particular network and are not safety, malware, reputation, or ownership conclusions.
  • IPv6 has no IPv4-style broadcast address. Address counts are exact totals and never universally subtract two.