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CIDR / IP Calculator

Recon & Discovery Free · No sign-up

IPv4 & IPv6 subnet math for scoping - expand, aggregate, split, classify and export - entirely in your browser.

Try it now No sign-up required. Runs entirely in your browser.
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Summary
Addresses

What is CIDR / IP Calculator?

CIDR / IP Calculator is the network-math companion for scoping. Paste a CIDR, a single IP, an address range or a netmask (IPv4 or IPv6) and it returns the network and broadcast addresses, usable host range, masks, total counts, and the reverse-DNS (PTR) name.

Give it several lines or a messy scope list and it aggregates them into the minimal set of covering CIDRs; give it one block and it can split it into smaller subnets. It also flags the RFC scope of an address (private, CGNAT, loopback, documentation, multicast or public) so you can sanity-check what is actually in-scope.

It runs entirely in your browser - instant, private, and works offline once the page is loaded.

What it computes

  • IPv4 & IPv6 - full BigInt-accurate IPv6 alongside IPv4.
  • Flexible input - CIDR, single IP, a-b ranges, or dotted netmask notation.
  • Aggregation - merge a list of blocks/ranges into the minimal covering CIDRs.
  • Subnet splitting - divide a block into smaller /N subnets.
  • RFC scope - private / CGNAT / loopback / documentation / multicast / public.
  • Reverse DNS - in-addr.arpa and ip6.arpa names for recon.
  • Export - copy/download the address list or copy a canonical nmap/masscan target.

Where it fits in your workflow

  • →Translate an in-scope CIDR into the exact IPs you are allowed to test.
  • →Aggregate a sprawling scope list into a clean set of CIDRs.
  • →Confirm whether an address is private/CGNAT (likely out of external scope) or public.
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At a glance

CategoryRecon & Discovery
RunsIn your browser
Token cost Free - no tokens
Access No login needed
Status● Live

Frequently asked questions

Does it support IPv6?

Yes - IPv6 is fully supported with BigInt-accurate math, including ::-compression, embedded IPv4, prefix masks, scope classification and ip6.arpa reverse names.

Can it turn a list of ranges into CIDRs?

Yes - paste multiple lines or an a-b range and it merges overlapping entries and emits the minimal set of covering CIDRs, with a total address count.

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