How many subnets can I create in an AWS VPC?

AWS allows up to 200 subnets per VPC by default. You can request a quota increase if your architecture requires more, though most designs use between 6 and 20 subnets across availability zones.

Should public and private subnets be the same size?

Typically no. Private subnets usually need more IP addresses because they host application servers, containers, and databases, while public subnets primarily hold load balancers and NAT gateways. A common pattern is /20 for private subnets and /24 for public subnets.

Can subnets span multiple availability zones?

No. Each AWS subnet exists in exactly one availability zone. To achieve high availability, you create matching subnets in multiple AZs and distribute your resources across them.

Subnet Planner

NetworkingAWS

Plan and visualize subnet allocation within a VPC CIDR block.

Subnet Configuration

VPC CIDR

Number of Subnets (1-16)

Subnet Prefix Length

Raw Output

Output will appear here...

About This Tool

The Subnet Planner helps you divide a VPC CIDR block into multiple subnets with precise control over sizing, availability zone assignment, and naming. Manually slicing IP ranges is error-prone and tedious, especially when you need public, private, and database subnets across multiple AZs. This tool visualizes the allocation, detects overlaps, and shows remaining free space so you can design production-ready network layouts in minutes.

When to Use This Tool

•Designing a multi-AZ VPC layout with separate public, private, and data subnets in each availability zone.
•Splitting a secondary CIDR block into subnets for a new microservice tier without overlapping existing allocations.
•Planning subnet sizes that leave room for future growth while meeting minimum host-count requirements.
•Generating subnet documentation for architecture review boards or compliance audits.

Frequently Asked Questions

How many subnets can I create in an AWS VPC?: AWS allows up to 200 subnets per VPC by default. You can request a quota increase if your architecture requires more, though most designs use between 6 and 20 subnets across availability zones.
Should public and private subnets be the same size?: Typically no. Private subnets usually need more IP addresses because they host application servers, containers, and databases, while public subnets primarily hold load balancers and NAT gateways. A common pattern is /20 for private subnets and /24 for public subnets.
Can subnets span multiple availability zones?: No. Each AWS subnet exists in exactly one availability zone. To achieve high availability, you create matching subnets in multiple AZs and distribute your resources across them.

Related Learning Guides

AWS Networking Deep Dive30 min read
VPC Architecture Patterns28 min read

Disclaimer: This tool runs entirely in your browser. No data is sent to our servers. Always verify outputs before using them in production. AWS, Azure, and GCP are trademarks of their respective owners.