CIDR Calculator
Calculate IPv4 network boundaries, subnet and wildcard masks, address ranges, and host counts from CIDR notation.
Enter IPv4 CIDR notation like 10.0.0.1/16 or 192.168.1.1/24.
Understanding CIDR Notation and Subnets
CIDR stands for Classless Inter-Domain Routing. It is a compact way to represent IP ranges and subnet masks using slash notation.
Network engineers, DevOps teams, cloud administrators, hosting providers, and infrastructure engineers commonly use CIDR blocks while configuring VPCs, firewalls, VPNs, routing rules, Docker networks, Kubernetes clusters, and internal infrastructure.
CIDR calculations help determine usable IP ranges, broadcast addresses, network boundaries, and subnet capacities before deploying systems into production.
Common CIDR Examples
192.168.1.10/24 10.0.0.1/16 172.16.10.5/20 192.168.100.10/30
Practical CIDR Use Cases
- Designing internal VPC subnet ranges in AWS, Azure, or GCP.
- Planning Kubernetes cluster node and pod networking.
- Preparing firewall allowlists and routing tables.
- Troubleshooting overlapping subnet ranges.
- Allocating smaller subnet blocks for infrastructure environments.
- Understanding usable host capacity before deployment.
Frequently Asked Questions
What is CIDR notation?
CIDR notation combines an IP address with a subnet prefix length, such as /24 or /16, to represent subnet ranges efficiently.
What does /24 mean?
A /24 subnet means the first 24 bits are used for the network portion, leaving 8 bits for host addresses.
Why are usable hosts fewer than total hosts?
Traditional IPv4 subnets from /0 through /30 reserve one network address and one broadcast address. A /31 can use both addresses on a point-to-point link, while a /32 represents one address.
How are /31 and /32 ranges counted?
This calculator treats a /31 as two usable point-to-point addresses and a /32 as one individual address. Some older systems may present /31 ranges differently.
Is this CIDR calculator processed on the server?
No. All subnet calculations happen directly inside your browser. Your IP ranges are not uploaded to a server.