IP Subnet Calculator
Calculate IPv4 network boundaries, masks, usable hosts and address capacity from CIDR notation.
Calculate an IPv4 subnet
CIDR and subnet masks
The CIDR prefix counts network bits. A /24 corresponds to 255.255.255.0, leaving eight host bits and 256 total addresses. The network and broadcast addresses bound the conventional host range.
Special prefixes
A /30 conventionally provides two usable hosts. A /31 provides two endpoint addresses on an RFC 3021 point-to-point link, and a /32 identifies one host route. The calculator handles these explicitly rather than always subtracting two.
Frequently asked questions
What is CIDR notation?
CIDR combines an address and prefix length, such as 192.0.2.10/24. The prefix says how many leading bits identify the network.
How are /31 networks handled?
Under RFC 3021, both addresses in a /31 can be used on a point-to-point link, so the calculator reports two usable addresses.
What does /32 mean?
A /32 identifies exactly one IPv4 address rather than a conventional multi-host subnet.
What is a wildcard mask?
It is the bitwise inverse of the subnet mask and is commonly used in network access-control syntax.