CIDR to IP Range & Subnet Calculator
Enter a CIDR block to instantly calculate the network address, broadcast address, usable IP range, subnet mask, wildcard mask and total hosts. Also split a CIDR into smaller subnets.
10.0.0.0/24 in the input fieldWhat is a CIDR Calculator?
A CIDR (Classless Inter-Domain Routing) calculator converts IP address blocks written in CIDR notation — such as 10.0.0.0/24 — into their constituent details: network address, broadcast address, subnet mask, usable host range, and total host count. For DevOps and network engineers, this is an essential daily tool when designing VPCs, writing firewall rules, or planning Kubernetes pod networks.
Before CIDR was introduced in 1993, IP address allocation relied on rigid class-based boundaries (Class A, B, C) that wasted enormous blocks of address space. CIDR replaced this with variable-length subnet masking (VLSM), allowing networks of any size to be precisely carved from the available IPv4 space. Understanding CIDR is foundational to modern cloud networking, routing protocols, and security group configuration.
When to Use This Tool
- VPC design: Calculate the right CIDR block size before provisioning an AWS VPC, Azure VNet, or GCP network to ensure you have enough address space for current and future workloads.
- Firewall and security group rules: Quickly verify which IP addresses fall within a given CIDR block when writing ingress/egress rules for cloud security groups or on-premise firewalls.
- Kubernetes networking: Determine appropriate pod CIDR and service CIDR ranges so they don't overlap with each other, the node network, or external corporate networks.
- Subnet planning: Split a large address block into smaller subnets for different availability zones or tiers (public, private, database) and confirm host counts before deployment.
How It Works
The calculator takes an IP address and prefix length (the number after the slash), then applies bitwise AND with the subnet mask to derive the network address. The broadcast address is found by OR-ing the host bits to all ones. Usable host count is 2(32 - prefix) minus 2, accounting for the reserved network and broadcast addresses. All arithmetic is performed client-side in your browser — no data ever leaves your machine.
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation like 10.0.0.0/24 defines an IP address range. The number after the slash indicates how many bits are fixed (the network part), determining how many host addresses are available. The remaining bits form the host portion and can vary freely within that block. For example, a /24 fixes the first 24 bits, leaving 8 bits for hosts — yielding 256 total addresses (254 usable after reserving network and broadcast).
What is the difference between /24 and /16?
A /24 subnet provides 254 usable host addresses and is the most common subnet size for a single team or application tier. A /16 provides 65,534 usable addresses and is typical for an entire VPC or large corporate network segment. Each step up in prefix length (e.g., from /24 to /25) halves the available hosts, while each step down doubles them. Choosing the wrong size at VPC creation time is difficult to fix later, so it pays to calculate carefully upfront — AWS, for instance, allows VPC CIDR ranges from /16 to /28.
How do I choose the right CIDR block for a VPC or Kubernetes cluster?
For a VPC, choose a private RFC 1918 range (10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16) and size it generously to accommodate future growth — a /16 is a common starting point for production environments, giving you 65,534 addresses you can divide into subnets per availability zone. For Kubernetes, ensure the pod CIDR does not overlap with your VPC CIDR or any peered networks; a dedicated /16 or /17 for pods is common for clusters with hundreds of nodes, since each node is typically allocated a /24 slice from that range. Always check for CIDR conflicts with VPN ranges, Direct Connect networks, and other peered VPCs before finalising your design.