CIDR Calculator

Binary view

Split into subnets at prefix

Is an IP in this network?

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Protocol

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Usable hosts

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Mask

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Prefix

What is this CIDR calculator?

This is a free online CIDR / subnet calculator that breaks any IPv4 or IPv6 CIDR block into its network, broadcast and usable host range, instantly — fully client-side, so confidential infrastructure topologies never leave your browser.

How do I calculate a subnet from a CIDR block online?

Enter a CIDR like 10.0.0.0/24 and the calculator shows the network address, broadcast, subnet mask, first and last usable host, and the total number of addresses — all instantly, locally in your browser.

Key features

IPv4 and IPv6 in one

Same input box accepts both 192.168.0.0/22 and 2001:db8::/48 and computes the matching subnet properties.

Usable host range

Reports first and last assignable host, excluding network and broadcast (IPv4) or anycast (IPv6) as appropriate.

Mask formats

Shows the prefix length, dotted-decimal mask and wildcard / inverse mask for use in ACLs and route maps.

100% client-side

Bit-level arithmetic runs in JavaScript inside your tab. Your network layout is never uploaded.

How to use it

Type the CIDR (e.g. 192.168.10.0/26 or fd00::/8) into the input. The calculator displays the network address, broadcast, subnet mask, first/last usable host, hex form and total address count. Use the wildcard mask field directly in your firewall or router ACLs. It also flags the address type (private, loopback, CGNAT, public and more), checks whether an IP falls inside the range, shows a binary breakdown and splits the block into smaller subnets.

Frequently asked questions

Does it support /31 and /32 prefixes?

Yes. /31 is recognised as a point-to-point link and /32 as a single host; usable host ranges are reported accordingly.

Are IPv6 prefix sizes capped?

No. The calculator handles the full /0 to /128 IPv6 range using arbitrary-precision bit math.

Is the data sent anywhere?

No. All arithmetic happens in your browser; no IP, CIDR or network description ever leaves the page.

Tooljar implements RFC 4632 (IPv4) and RFC 4291 (IPv6) prefix arithmetic with explicit big-integer handling, so the host counts and ranges are exact even for /0 IPv6 blocks.