Calculate IP subnet details including network address, broadcast address, host range, and CIDR notation.
Enter an IPv4 address and a prefix length, and this tool returns the facts that define the subnet containing that address: the network address, the broadcast address, the usable host range, and the same mask written as CIDR notation. Everything follows from one bit-level rule - the prefix fixes how big the block is, and the address you typed only decides which block you are in. The surprise most people hit: the subnet does not start at the address they entered, and the usable host count is always two less than the block size.
A concrete input and expected output from the current implementation.
Input
192.168.1.37/26
Expected output
Network address: 192.168.1.0 Broadcast address: 192.168.1.63 Usable host range: 192.168.1.1 - 192.168.1.62 Usable hosts: 62 Netmask: 255.255.255.192 (/26)
A /26 prefix fixes the block at 64 addresses (2^(32-26)), and 37 falls inside the block that starts at 192.168.1.0 and ends at 192.168.1.63. The first and last addresses are reserved as network and broadcast, leaving 62 usable addresses.
The prefix length is the number of leading bits every address in the block shares. The tool aligns the address you entered to that boundary: the network address is the block's first address, the broadcast address is its last, and the usable range sits between them. Block size is 2^(32 - prefix), so each prefix one bit shorter doubles the block.
Each result is paired with its meaning: network address, broadcast address, the usable host range between them, and the mask written both as a /prefix and as a dotted-decimal mask. Two prefixes break the usual pattern: a /31 uses both addresses for hosts on point-to-point links (RFC 3021), and a /32 describes one single host.
Because the first and last addresses are reserved, not merely discouraged. The network address identifies the block itself and the broadcast address reaches every host in it, so neither can belong to a device. Usable count is always block size minus two - 62 for a /26, 14 for a /28 - with /31 and /32 as the exceptions.
The outputs the tool produces - network address, broadcast address, usable host range - are IPv4 concepts. IPv6 has no broadcast address, uses 128-bit addresses in a different notation such as 2001:db8::1/64, and counts hosts differently. If your task is IPv6 planning, use a calculator that states IPv6 support rather than assuming this one extends to it.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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