Subnet Calculator

Subnetting is the practice of dividing a larger IP network into smaller, more manageable sub-networks (subnets). Every IP address is divided into two parts: the network portion (which identifies the subnet) and the host portion (which identifies a specific device on that subnet). The subnet mask determines where this division occurs. Our Subnet Calculator takes an IP address and a CIDR prefix length (like /24) or subnet mask (like 255.255.255.0) and instantly calculates all the critical details: network address, broadcast address, first and last usable host addresses, total number of hosts, and the wildcard mask used in access control lists.

Understanding CIDR Notation

CIDR (Classless Inter-Domain Routing) notation is the modern way to express subnet masks. It appends a slash and a number to an IP address — for example, 192.168.1.0/24. The number after the slash indicates how many bits of the 32-bit address are used for the network portion. A /24 means the first 24 bits are the network part and the remaining 8 bits are for hosts, giving 254 usable addresses (2^8 - 2, minus the network and broadcast addresses). A /16 gives 65,534 hosts. A /32 represents a single host address. Understanding CIDR is essential for network engineers, system administrators, and anyone preparing for networking certifications.

Common Subnet Masks

The most commonly used subnet masks are /8 (255.0.0.0) for very large networks with over 16 million hosts, /16 (255.255.0.0) for large enterprise networks with 65,534 hosts, /24 (255.255.255.0) for typical local networks with 254 hosts, and /30 (255.255.255.252) for point-to-point links with just 2 usable hosts. In cloud computing, /28 and /27 subnets are popular for small server groups. When designing networks, always plan for growth by choosing a subnet size larger than your current needs.