Subnet Calculator
Split a network into evenly sized subnets and plan address allocation.
Nothing split yet
Enter a parent network and choose how to divide it. Splitting by hosts picks the smallest prefix that still fits your requirement.
Runs entirely in your browser. Your data isn't uploaded — this page makes no network request with anything you type, which you can verify in your browser's network tab. How this works.
What is the Subnet Calculator?
Address planning is the part of building a VPC that is genuinely hard to redo later. You start with a block, decide how to divide it across availability zones and tiers, and need each subnet to be big enough without wasting the space you will want for the next environment.
This calculator splits a network two ways: by target prefix length, giving you evenly sized subnets, or by required host count, choosing the smallest prefix that fits. Either way you get a table of every resulting subnet with its range, ready to paste into a plan or a Terraform variable.
How to use it
- Enter the parent network in CIDR notation.
- Choose how to split it: by new prefix length, by number of subnets, or by hosts needed per subnet.
- Review the table of resulting subnets and their address ranges.
- Copy the list, or export it as CSV or a Terraform-friendly list.
Example
Splitting a /24 into four /26 subnets.
192.168.10.0/24 → /26
192.168.10.0/26 .1 – .62 62 hosts 192.168.10.64/26 .65 – .126 62 hosts 192.168.10.128/26 .129 – .190 62 hosts 192.168.10.192/26 .193 – .254 62 hosts
Features
- Split by prefix length, subnet count or required hosts per subnet
- Per-subnet network, range, broadcast and usable host count
- AWS mode that accounts for the five reserved addresses per subnet
- Remaining-space summary so you can see what is left for future growth
- CSV and Terraform list export