Networking

VLSM Calculator

Allocate different subnet sizes to match a list of device counts.

Calculations run in your browser. The tool does not send your inputs to a server.

01Your inputs

Local workspace

Start with the sample below, or enter your own values.

IPv4 / prefixA whole-number IPv4 prefix from 0 to 32. A larger prefix describes a smaller block.

Required hosts, one per linePut each entry on its own line, following the example format.

02Your result

Your result will appear here. Choose an action after checking your inputs.

A quick guide

How to use this tool

Check the example and the unit beside each input.
Enter your values and choose Calculate.
Review the result and assumptions, then copy what you need.

Reset example restores the starting values. Clear removes text and number inputs, returns choices to their first valid option, and removes the result.

Reference guide

Explanation and worked examples

VLSM means Variable Length Subnet Mask. Larger requests are allocated first. The parent network must have room for every allocation.

Use in day-to-day IT work

Allocate several VLANs inside a parent block before updating IPAM.

Checks before applying the result

Include gateways, static reservations and growth in each required host count. Output requirement numbers refer to the original input order.
This conventional LAN allocator reserves network and broadcast addresses; it does not allocate /31 links. Check overlap with networks outside the supplied parent block.

New to the terminology?

CIDR: An address block written with a slash and prefix length, such as /24.
Prefix: The number of address bits fixed to identify a network.
Mbps: Millions of bits per second. Divide by eight to compare with MB/s.

Keep exploring

How calculations work and where the models stop →