How it works
The calculator keeps the parent VPC network intact, then adds enough subnet bits to split the range into equal blocks.
Subnet prefix: parent prefix + log2(subnet count)
Subnet size: 2^(32 - subnet prefix)
Networking / United States
AWS VPC subnet planner
Start from a VPC CIDR, choose how many equal subnets you want, and see the CIDR, subnet mask, network, broadcast, usable range, and AWS usable IP count for each subnet.
Plan equal subnets
Equal subnet splitting needs a power-of-two count like 2, 4, 8, or 16.
Subnet breakdown
Each subnet card shows the CIDR, mask, network and broadcast addresses, usable range, and AWS usable IP count.
Assumptions
- Works with IPv4 CIDR input only.
- Equal-sized splitting requires 2, 4, 8, 16, and so on.
- AWS VPC mode warns when the result is outside the supported subnet range.
Quick example
10.0.0.0/16 split into 4 subnets produces four /18 ranges.
That means 10.0.0.0/18, 10.0.64.0/18, 10.0.128.0/18, and 10.0.192.0/18.
Common mistakes
- Using a subnet count that is not a power of two.
- Forgetting AWS reserves the first four and last IP in each subnet.
- Choosing subnet sizes outside the AWS VPC supported range.
- Confusing the parent VPC CIDR with each child subnet CIDR.