How to Read and Use a CIDR Cheat Sheet
A CIDR cheat sheet is one of the most essential tools for any network engineer, system administrator, or IT professional working with IP addressing and subnetting. It provides an at-a-glance reference for every possible IPv4 subnet, mapping CIDR prefixes (ranging from /0 to /32) to their corresponding dotted-decimal subnet masks, total addresses, usable host counts, and wildcard masks. Rather than manually converting binary to decimal every time you need to determine a subnet size, a well-organized cheat sheet lets you instantly see that a /24 network contains 256 addresses with 254 usable hosts, or that a /29 provides only 6 usable IPs — a common size for IoT or management VLAN deployments.
The concept of CIDR (Classless Inter-Domain Routing) was introduced in 1993 to solve two major problems with the original classful IP addressing system. Under the old system, organizations were assigned either a Class A, B, or C block regardless of their actual needs, leading to massive waste of IPv4 address space. A Class A block contained over 16 million addresses — far too many for most organizations — while a Class C block contained only 254 addresses, forcing larger companies to request multiple blocks. CIDR replaced this rigid system with variable-length subnet masking (VLSM), allowing any prefix length from /0 to /32. The CIDR cheat sheet on this page covers every possible prefix length from /0 (0.0.0.0, the default route) to /32 (a single host), so you always have the exact information you need.
To use the cheat sheet, locate your desired prefix length in the first column and read across to find the subnet mask, usable host count, and wildcard mask. For example, a /27 network (mask 255.255.255.224) provides 30 usable addresses, making it a popular choice for branch offices and remote site VLANs that need fewer than 30 devices. A /30 network is the standard for point-to-point links with exactly 2 usable hosts. A /23 network provides 510 usable addresses — ideal for larger departments that need more than a single /24 but less than a /22. The filter input above the table lets you quickly narrow down entries by typing a prefix, mask, or host count, which is especially useful when working with large IPAM spreadsheets or cloud subnet allocation plans.
This CIDR cheat sheet also includes the three RFC 1918 private IP ranges displayed at the top. Understanding these ranges is critical because private addresses are used extensively in enterprise networks, home routers, and cloud VPCs. The 10.0.0.0/8 block is the largest private range, used by large organizations and cloud providers like AWS, Azure, and GCP for their virtual networks. The 172.16.0.0/12 block is commonly deployed in medium-sized business networks and educational institutions. The 192.168.0.0/16 block is the most recognizable range, used by virtually every consumer router on the market. Additionally, the cheat sheet lists special-purpose addresses: 127.0.0.0/8 for loopback (localhost), 169.254.0.0/16 for APIPA (link-local auto-configuration when DHCP fails), and 224.0.0.0/4 for multicast traffic such as routing protocol updates.
The legacy IP address classes are also included for historical reference. Although CIDR has made classful addressing obsolete, understanding that Class A spans 1.0.0.0 through 126.255.255.255, Class B covers 128.0.0.0 through 191.255.255.255, and Class C ranges from 192.0.0.0 through 223.255.255.255 is still valuable when reading older network documentation or configuring legacy equipment. The default subnet masks — /8 for Class A, /16 for Class B, /24 for Class C — are the foundation that modern CIDR notation builds upon. Whether you are studying for the CompTIA Network+, Cisco CCNA, or AWS Certified Advanced Networking exam, or simply troubleshooting a connectivity issue on your home network, this CIDR cheat sheet puts all the essential subnetting information at your fingertips.