CIDR Calculator — Free Online CIDR Subnet Range Calculator
Calculate IP ranges, host counts, and network details from CIDR notation — list all IPs in small ranges.
Jump to tool ↓Frequently Asked Questions
CIDR Notation: Modern IP Address Range Management
CIDR replaced the original class-based IP addressing system (Class A, B, C) in 1993 to solve the rapid depletion of IPv4 addresses. By allowing arbitrary prefix lengths instead of fixed 8/16/24-bit boundaries, CIDR enabled more efficient allocation of IP address space to organizations based on their actual needs.
Today, CIDR is foundational to cloud networking. AWS Security Groups, Azure NSGs, GCP firewall rules, and Kubernetes network policies all use CIDR blocks to define network access rules. Understanding how to read and calculate CIDR ranges is essential for any infrastructure or DevOps role.
Common CIDR use cases: VPC subnet sizing (/20 for 4096 addresses), firewall rule specificity (/32 for single-IP rules), BGP route aggregation (combining multiple smaller routes into a single larger prefix), and Kubernetes pod/service CIDR allocation (/16 providing 65536 pod addresses).
Standards & References
Built and maintained by DevDecode. This tool processes your input in your browser; it is not uploaded for processing. Found an issue? Let us know.
Related Tools
Related Guides
How to Fix Slow DNS Lookups: 6 Proven Fixes
Slow DNS lookups delay every website you visit. Learn how to fix slow DNS — switch to a faster resolver, flush the cache, rule out VPN/antivirus interference, and diagnose the problem with dig and nslookup.
NetworkWhat Is a Static IP Address (vs Dynamic)?
A static IP address never changes, unlike a dynamic one assigned by DHCP. Learn the pros, cons, security considerations, and when you actually need a static IP.
NetworkWhat Is an IP Address? IPv4 vs IPv6 Explained
An IP address is a unique number identifying a device on a network. Learn IPv4 vs IPv6, public vs private, static vs dynamic, and how to read an IP address.
NetworkCIDR Notation Explained: How to Read 10.0.0.0/24
CIDR notation replaced classful networking 30 years ago but still trips people up. Here's how the slash works, how to count hosts, and how to spot a bad subnet.