VPC Subnet Calculator
What is this tool?
Planning your AWS VPC network from scratch is one of those things that sounds simple until you actually sit down and try to do it.
How many subnets do you need? What CIDR block should you use? Which subnets go in which Availability Zone? If you are just starting out with AWS, these questions can feel overwhelming fast.
This free VPC Subnet Calculator walks you through the whole process step by step. You define your subnets, pick your VPC size, assign them to Availability Zones and get your CIDR ranges calculated instantly. No guesswork, no manual maths.
Who is this for?
This tool is built for anyone learning AWS networking, whether you are studying for your AWS Solutions Architect exam, building your first VPC, or just trying to understand how subnets and CIDR blocks actually work in practice.
You do not need any prior networking experience to use it. Just follow the steps and the calculator does the rest.
How to use it:
- Define Subnets: choose how many subnets you need and what size they should be
- VPC Config: set your overall VPC CIDR block
- Assign AZs: distribute your subnets across Availability Zones
- Calculate: get your final CIDR ranges instantly
Just a practical tool to help you learn by doing.
VPC Subnet Calculator
Master AWS networking by building it — define subnets, pick your VPC size, assign to AZs, and get real CIDRs instantly.
Educational use only · Not affiliated with Amazon Web Services
Subnet Size Reference: How many IPs do I need?
Not sure what prefix to use? Enter your required usable IPs below and we'll show the smallest valid AWS subnet that fits. Use this as a guide when filling in Step 1.
Quiz Mode
Toggle quiz mode on before calculating — results will be hidden and you'll guess the CIDR prefix for each AZ yourself. A great way to test your understanding of IP math.