IP Subnet Calculator

IP Subnet Calculator — Instantly Compute Network Address, Host Range, and Subnet Details

Subnetting is one of the fundamental skills in network engineering and cloud infrastructure work. Whether you are designing a VPC in AWS, configuring OSPF areas on a corporate network, writing ACL rules, or setting up a home lab, you need to quickly calculate the network address, broadcast address, usable host range, subnet mask, and wildcard mask for any given CIDR block. This calculator does all of that instantly from any IPv4 address in CIDR notation.

How to use this calculator

Enter any IPv4 address in CIDR notation — for example, 192.168.1.0/24 or 10.0.0.0/16 — or with a dotted mask such as 192.168.1.0 255.255.255.0. The calculator immediately shows the network address (first address in the subnet), broadcast address (last address), usable host range (first and last assignable IP addresses), subnet mask in dotted-decimal notation, wildcard mask (inverse of subnet mask, used in ACLs and OSPF), total number of addresses, number of usable hosts, IP address class (A, B, C, or special), and whether the address falls in a private range (RFC 1918) or public, and names the special ranges (loopback, link-local, carrier-grade NAT, documentation, multicast). Click any row in the common subnets reference table to load that prefix for the address you entered.

Understanding CIDR notation and subnet math

CIDR (Classless Inter-Domain Routing, defined in RFC 4632) notation expresses an IP address and its prefix length together — the /24 in 192.168.1.0/24 means the first 24 bits are the network prefix, leaving 8 bits for host addresses. With 8 host bits, there are 2^8 = 256 total addresses, minus 2 for the network and broadcast addresses, giving 254 usable hosts. A /16 gives 2^16 = 65,536 addresses (65,534 usable). A /30 gives 4 addresses (2 usable) — the minimum for a point-to-point link. The wildcard mask (e.g., 0.0.0.255 for a /24) is the bitwise inverse of the subnet mask and is used in Cisco ACL rules and OSPF network statements to specify which bits to match.

Who uses this tool

Network engineers use it when designing IP addressing schemes for enterprise networks or planning VPC CIDR ranges in cloud deployments. Systems administrators use it when configuring network interfaces and need to verify their subnet mask is correct. Security engineers use it when writing firewall ACL rules that require wildcard masks. Students studying for CCNA, CompTIA Network+, or AWS certifications use it to verify their manual subnetting calculations and build intuition for common subnet sizes.

Privacy and data handling

All subnet calculations are performed entirely in your browser using JavaScript bitwise operations — no IP addresses or network configurations are sent to any server.