IP & Network
Subnet / CIDR Calculator
Calculate network boundaries and address counts from an IPv4 or IPv6 address with a CIDR prefix. No network request is made.
Calculate a subnet
How CIDR prefixes work
CIDR writes an address followed by the number of leading network bits. In IPv4, /24 leaves eight host bits and therefore contains 256 total addresses. Longer prefixes describe smaller networks.
/31 and /32 are special
A traditional IPv4 subnet reserves network and broadcast addresses, but a /31 point-to-point link can use both addresses under RFC 3021. A /32 identifies a single address. The calculator handles these cases instead of always subtracting two.
IPv6 has no broadcast address
IPv6 uses multicast rather than an IPv4-style broadcast address. Its enormous address counts describe the mathematical range, not a recommendation to assign every address.
What this result means
The boundaries are mathematical results for the prefix. Traditional IPv4 usable-host rules have /31 and /32 exceptions, while IPv6 has no broadcast address and assignment policy determines actual use.