CIDR Calculator

Enter an IPv4 CIDR block to get full subnet details instantly.

CIDR Notation
Quick examples
10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 192.168.1.0/24 10.10.10.64/26 203.0.113.0/30

About CIDR Notation

CIDR (Classless Inter-Domain Routing) notation describes a block of IP addresses as address/prefix. The prefix length (0–32) specifies how many bits are fixed for the network portion; the remaining bits identify individual hosts within that subnet.

For example, 192.168.1.0/24 has 24 network bits and 8 host bits, giving 256 total addresses (254 usable hosts).

Fields explained

Network Address: The first address in the block (all host bits = 0). Not assignable to a host.

Broadcast Address: The last address in the block (all host bits = 1). Not assignable to a host.

Subnet Mask: The network bits expressed as an IPv4 address (e.g. 255.255.255.0 for /24).

Wildcard Mask: The inverse of the subnet mask. Used in ACL configurations.

Usable Hosts: Total hosts minus 2 (network and broadcast). A /31 and /32 are special cases.

IP Class: The traditional classful class (A/B/C/D/E) based on the first octet.

Frequently asked questions

What is a /32?
A /32 is a host route with only a single IP address. It is used for loopback addresses and for specifying a single host in routing tables. It has 1 total address and 0 usable hosts (no broadcast or network address concept).
What is a /31?
A /31 has 2 IP addresses and is used for point-to-point links (RFC 3021). Both addresses are usable; there is no network or broadcast address.
Does the input IP need to be the network address?
No. You can enter any host address in the block (e.g. 192.168.1.45/24) and the calculator will show the network the host belongs to.

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