Quick start
How to use the subnet calculator
- Enter an IPv4 address, such as
192.168.1.42. - Enter its CIDR prefix as a number from
0to32. - Select Calculate subnet to update every result.
Reading the answer
What the subnet results mean
Network and broadcast addresses
The network address identifies the subnet itself. The broadcast address reaches all hosts on a traditional IPv4 subnet and normally cannot be assigned to one device.
Subnet and wildcard masks
The subnet mask marks the network bits with ones. The wildcard mask is its inverse and is often used in access-control lists.
Usable IP range
The first and last usable addresses show the normal host assignment range after reserved network and broadcast addresses are excluded.
Total and usable addresses
Total addresses include every address in the block. Usable host count applies modern exceptions for /31 links and /32 host routes.
Small networks
How /31 and /32 are handled
On a point-to-point link, RFC 3021 section 2.1 allows both addresses in a /31 to be used because a traditional network and broadcast address are unnecessary. A /32 identifies one specific address, commonly as a host route. This calculator reports two usable addresses for a /31 and one for a /32.
Common questions
IPv4 subnet calculator FAQ
What does a subnet calculator show?
It turns an IP address and CIDR prefix into the network boundaries, masks, usable range, and address counts needed to understand that subnet.
How many usable hosts are in a /24?
A /24 contains 256 total addresses. On a normal subnet, 254 are usable by hosts because the network and broadcast addresses are reserved.
Are /31 and /32 addresses usable?
A /31 can use both addresses on a point-to-point link under RFC 3021. A /32 identifies one address, commonly as a host route.