Subnet & CIDR Tools

SubnetTool provides free, cloud-aware subnet and CIDR calculators designed for modern infrastructure teams.

Whether you are planning:

Azure Kubernetes Service (AKS) clusters
Azure Red Hat OpenShift (ARO) environments
Amazon EKS (AWS Kubernetes) deployments
Google Kubernetes Engine (GKE) clusters
AWS or GCP subnet ranges
CIDR to IP range validation
Usable IP capacity calculations

These tools help you move from rough IP estimates to deployment-ready subnet sizing.

The goal is not to publish generic calculators for every topic. The goal is to make cloud subnetting and Kubernetes IP planning easier to reason about, especially in places where textbook subnet math stops being enough.

Kubernetes Subnet Calculators (AKS, EKS, GKE, ARO)

Cloud-native environments introduce new subnet challenges:

Azure reserves 5 IP addresses per subnet
AWS reserves 5 IP addresses per subnet
GCP reserves 4 IP addresses per subnet
Some Kubernetes CNIs consume pod IPs directly from subnets
Kubernetes scaling multiplies IP requirements quickly

Our Kubernetes subnet planners calculate:

Node subnet size
Pod CIDR sizing
Growth buffer impact
Reserved IP impact
Recommended CIDR prefix lengths

These tools are most useful when you are still deciding on architecture, growth assumptions, and provider-specific networking behavior. Once a cluster or subnet is already live, fixing a bad CIDR choice is much more expensive.

Use the calculators this way:

Start with Kubernetes Pod CIDR Calculator for provider-neutral or vanilla Kubernetes planning.
Use Cloud Kubernetes Subnet Planner when you need AKS, EKS, GKE, or ARO-specific subnet behavior.

If you’re unsure how networking differs across providers, start here:

→ Kubernetes Networking Comparison (AKS vs EKS vs GKE vs ARO)

Available Tools

Kubernetes Subnet Planning

→ Cloud Kubernetes Subnet Planner (AKS, EKS, GKE, ARO)
→ Kubernetes Pod CIDR Calculator
→ AKS Subnet Calculator
→ ARO Subnet Calculator
→ EKS Subnet Calculator
→ GKE Subnet Calculator

Cloud & CIDR Utilities

Why Use Cloud-Aware Subnet Calculators?

Traditional subnet calculators do not account for cloud platform reservations.

For example:

A /24 in Azure does not give 256 usable IPs.
A /24 in AWS does not give 256 usable IPs.
Kubernetes overlay networking changes how pod IPs are allocated.

Incorrect assumptions lead to:

Node scaling failures
Pod scheduling issues
Worker subnet exhaustion
Expensive redesign during production

Using cloud-aware calculators helps prevent these mistakes before deployment.

If you are new to the site, the best starting points are:

Cloud Usable IP Calculator for provider-reserved address math
Subnet Calculator for classic IPv4 subnet splitting
Cloud Kubernetes Subnet Planner for provider-specific cluster sizing
Kubernetes Pod CIDR Calculator for provider-neutral node, pod, and service range planning

Subnet & CIDR Tools | Kubernetes, Azure, AWS & GCP Calculators