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CIDR Range Calculator

Work out a subnet: network, broadcast, host range and usable count.

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Quick Tool Overview

The CIDR Range Calculator derives every value a subnet has — network, broadcast, host range, wildcard and counts — using unsigned arithmetic, which is what a lot of subnet calculators get wrong at the top of the range.

What it does
Calculates everything about a subnet
You give it
A CIDR block, or an address and a mask
You get back
Network, broadcast, host range, counts and class
Best for
Network planning, firewall rules and VLSM
Developer Tools Free, unlimited use No sign-up Runs in your browser

About the CIDR Range Calculator

Enter a CIDR block, or an address and a mask, and every derived value is calculated: the network and broadcast addresses, the first and last usable host, the wildcard mask, the total and usable counts, and what kind of address range it is.

The arithmetic is done on unsigned values, which matters more than it sounds — JavaScript's bitwise operators work on signed 32-bit integers, so a /1 mask comes out negative and a lot of subnet calculators quietly get the top of the range wrong. The /31 and /32 special cases are handled properly too: a /31 is a point-to-point link with two usable addresses and no broadcast, and a /32 is a single host. There is also a divider for splitting a block into equal subnets.

Key features of the CIDR Range Calculator

Unsigned arithmetic

A /1 mask comes out negative under JavaScript’s bitwise operators, which is why many calculators break at the top of the range. This one does not use them.

The /31 and /32 cases

A /31 is a point-to-point link with two usable addresses and no broadcast; a /32 is a single host. Both are handled rather than producing a negative count.

Range classified

Private, loopback, link-local, carrier-grade NAT, documentation or public — with which RFC reserves it.

Wildcard mask

The inverse of the subnet mask, which is what a Cisco access list expects and what people most often compute backwards.

Subnet divider

Split a block into equal subnets of a longer prefix, with the range of each listed.

How to use the CIDR Range Calculator

  1. 1

    Enter a CIDR block

    Such as 192.168.1.0/24, or an address with a dotted mask.

  2. 2

    Read the range

    Network, broadcast, first and last host, and the usable count.

  3. 3

    Check the classification

    Whether the range is private, loopback, documentation or public.

  4. 4

    Divide it

    Split the block into equal subnets of a longer prefix.

Frequently asked questions

The first is the network address that identifies the subnet itself, and the last is the broadcast address. Neither can be assigned to a host, which is why a /24 has 256 addresses and 254 usable ones.

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