Visual Subnet Calculator

How to use it

1. Enter the network you want to plan, such as 10.0.0.0 with mask bits /16, then press Update. You can also paste CIDR notation like 10.0.0.0/16 into the address box.
2. Press Divide on any row to split it into two equal halves.
3. Press Join to merge a subnet with its neighbour back into the larger block.
4. The URL updates as you work, so bookmark it or use Copy Link to share the layout. Use Export CSV to take it into a spreadsheet.

AWS VPC Mode

AWS reserves five addresses in every VPC subnet. For 10.0.0.0/24 those are 10.0.0.0 (network), 10.0.0.1 (VPC router), 10.0.0.2 (Amazon DNS), 10.0.0.3 (future use) and 10.0.0.255 (broadcast). Subnets must be between /16 and /28, and rows outside that range are flagged.

Notes

Standard mode subtracts the network and broadcast addresses. A /31 is treated as a two-host point-to-point link (RFC 3021) and a /32 as a single host.