Subnet Calculator
Enter an IPv4 network in CIDR notation to see its subnet mask, usable host range, and other key details.
IPv4 Subnet Calculator
Calculate network details from IPv4 CIDR notation, such as 192.168.1.0/24.
Understanding CIDR and Subnetting
Classless Inter-Domain Routing (CIDR) replaced the older class-based system for allocating IP address space. Instead of fixed "Class A/B/C" ranges, CIDR uses a prefix length (for example, /24) to describe how many bits of the address represent the network portion.
Subnetting allows you to divide a larger address block into smaller networks. This helps isolate departments, improve routing efficiency, and reduce broadcast traffic.
Common IPv4 Subnet Sizes
/30
4 addresses, 2 usable
/29
8 addresses, 6 usable
/24
256 addresses, 254 usable
/16
65,536 addresses