🌐 IP Subnet Calculator

Subnetting is the process of splitting a larger IPv4 network into smaller, self-contained segments — and doing the binary math by hand is tedious and error-prone. This IP subnet calculator takes any IPv4 address and CIDR prefix length (from /8 down to /30) and instantly returns the network address, broadcast address, subnet mask, wildcard mask, first and last usable host, total address count, usable host count, and the legacy IP address class, all computed with real bitwise operations on the 32-bit integer representation of the address rather than a lookup table.

How It Works

The calculator first validates that the address you entered is a well-formed IPv4 dotted-decimal address (four octets, each 0–255). It then converts the address into a single 32-bit integer, and converts the CIDR prefix length into a subnet mask by setting the first N bits to 1 and the rest to 0. A bitwise AND between the address and the mask yields the network address; flipping the mask's bits (a bitwise NOT) gives the wildcard mask, and OR-ing that wildcard mask with the network address yields the broadcast address. The first usable host is one address above the network address, and the last usable host is one address below the broadcast address — except for /31 (both addresses usable per RFC 3021) and /32 (a single host).

Why It Matters

Correct subnetting prevents two very common and disruptive networking mistakes: assigning overlapping address ranges to different network segments, and under- or over-sizing a subnet so it either runs out of host addresses too soon or wastes a large block of address space that could serve other segments. Whether you're designing VLANs for an office, carving out address space for a cloud VPC, or just studying for a networking certification, seeing the exact network boundaries, broadcast address, and usable host range for a given prefix removes the guesswork from IP address planning.

Tips for Accurate Results

• Remember that the network address and broadcast address are never assignable to a device — only the range in between counts as usable hosts (with the /31 and /32 exceptions noted above).
• When you don't know the exact starting address of a subnet, enter any address within the range — the calculator will correctly determine the network address the same way a router would, using a bitwise AND with the mask.
• Use a longer prefix (e.g. /28 or /29) for small point-to-point or device-limited segments, and a shorter prefix (e.g. /22 or /16) for larger networks — this avoids wasting address space or running out of hosts.
• The IP address class shown is informational only; virtually all modern networks are addressed using CIDR rather than the old class-based (A/B/C) rules, so don't size a subnet based on its class.
• Double-check the CIDR prefix matches what's configured on your router or DHCP server — a mismatched mask is one of the most common causes of "can't reach this device" networking issues.