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Plan AWS VPC public and private subnet CIDR allocations across Availability Zones and export the result as CSV.
Step 1
Start with the VPC range and Region. The AZ count uses AWS published availability as a planning default.
Step 2
Public groups are allocated before private groups. Each group expands across the selected AZs.
Public subnet groups are allocated first for load balancers, NAT gateways, and ingress paths.
Private subnet groups are allocated after public ranges for application, data, and internal tiers.
Use this calculator to split an AWS VPC IPv4 CIDR block into public and private subnet ranges across Availability Zones. It validates AWS VPC sizing rules, accounts for reserved subnet IPs, and exports the allocation plan as CSV.
10.0.0.0/16.AWS reserves five IP addresses in every subnet, so a /24 has 251 usable IPv4 addresses instead of 256. The calculator also warns about 172.17.0.0/16 because AWS documents service conflicts with that range. If you want to estimate gateway, endpoint, NAT, and data transfer costs for this network design, use the Amazon VPC pricing calculator.
Building a compliant network foundation? Pair this with an AWS Landing Zone or AWS Security Review to turn the plan into secure VPC infrastructure, routing, guardrails, logging, and account-level controls.
Start from expected workload capacity and growth. Public subnets often use smaller ranges for load balancers and NAT gateways, while private application and data subnets usually need more address space.
AWS reserves the first four addresses and the last address in every subnet for network, router, DNS, future use, and broadcast-style reservation behavior.
Yes. AWS publishes Region-level AZ availability, but individual accounts can have constrained access to some AZs. Treat the Region AZ count as a planning default and confirm your actual account before deployment.
Yes. It allocates ranges sequentially inside the VPC block, aligns each subnet to its CIDR boundary, and stops with an error when the requested plan no longer fits.
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Next step
I build these tools to make AWS easier to manage. If this level of quality is what you want in your own cloud platform, Towards The Cloud can help with landing zones, infrastructure as code, security reviews, migrations, and cost optimization.