IP Subnet Calculator

Enter an IPv4 CIDR or an IP address with a subnet mask. See network address, broadcast, usable range, host count, wildcard mask, and more.

Input

CIDR notation

Format: IP/prefix such as 10.0.0.1/8 or 172.16.5.3/20.

IP address

Subnet mask

You can use dotted mask or prefix such as /24.

Results

IP address

Subnet mask

Wildcard mask

Network address

Broadcast address

First usable host

Last usable host

Total addresses

Usable hosts

IP class

Subnet this network

Supernet

New prefix

Example: split /16 into /20 networks.

#	Network	Range	Broadcast

Showing first {{ subnet.limit }} subnets for performance.

How it works

For IPv4 a subnet mask defines which part of the address is the network and which part is the host. A prefix such as /24 means the first 24 bits are the network. The calculator derives the network and broadcast addresses, then the usable host range.

Wildcard mask is the inverse of the subnet mask.
Usable hosts is normally total addresses minus two, one for network and one for broadcast. /31 and /32 are special and shown below.
Classful shows the traditional class based on the first octet. Modern networks use CIDR.

The Subnetter splits a supernet into equal smaller networks. It lists the first set for quick reference and can export a CSV.

Notes on /31 and /32

/31 is typically used for point to point links. There are two addresses and both are usable. No broadcast.

/32 represents a single host address.

Related tools

IPv4 subnetting explained

IPv4 addresses are 32 bits, written as four octets in dotted decimal. A subnet mask or prefix length tells you how many of those bits belong to the network. The remaining bits identify hosts inside that network.

Key outputs

Network address is the first address in the subnet.
Broadcast address is the last address. Hosts use it to reach all peers on the subnet.
Usable range sits between network and broadcast. These are the assignable host addresses.
Wildcard mask is useful in ACLs and some router syntax.

Practical tips

For small point to point links, /31 avoids wasting addresses.
Use the Subnetter to plan splits, for example carving a /24 into multiple /28s for lab VLANs.
Keep a record. Export the CSV and attach it to your change ticket so others can follow your plan.

If you would like IPv6 support, we can add it as an advanced tab with abbreviations, zero compression, and prefix maths.