CIDR Calculator

Calculate IPv4 and IPv6 subnets, hosts and ranges — every computation runs in your browser.

Binary view

Split into subnets at prefix

—

Protocol

—

Usable hosts

—

Mask

—

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.

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.

Toolbox 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.