CIDR calculator

Calculate IPv4 and IPv6 network boundaries, complete ranges, usable counts and masks.

172.96.192.0/18

IPv4

Input address: 172.96.254.97
Prefix length: /18
Total addresses: 16,384
Network address: 172.96.192.0
Last address: 172.96.255.255
Conventionally usable: 16,382
First usable: 172.96.192.1
Last usable: 172.96.255.254
Subnet mask: 255.255.192.0
Wildcard mask: 0.0.63.255

IPv4 /31 follows RFC 3021 and exposes both point-to-point addresses; /32 is one host. Other prefixes exclude network and broadcast addresses.

Understand prefixes and address counts

CIDR describes a network as an address and prefix length. Calculate boundaries, address counts and usable ranges for IPv4 or IPv6 directly in your browser.

Two examples, explainedCalculated examples

IPv4 network256 addresses

Address and prefix: 192.168.1.10/24
Network and final address: 192.168.1.0/24192.168.1.255

IPv6 network4 addresses

Address and prefix: 2001:db8::1/126
Network and final address: 2001:db8::/1262001:db8::3

Address countIPv4: 2^(32−prefix). IPv6: 2^(128−prefix).

Common questions

Why is the network address different from my input?

Your input can be any address in the block. The network address sets the host bits outside the prefix to zero.

Is this the number my cloud provider can allocate?

Not necessarily. Providers may reserve additional addresses. This tool calculates mathematical ranges, not provider-specific allocation policies.

How many addresses are in an IPv4 /24?

An IPv4 /24 contains 256 addresses. An ordinary subnet typically has 254 usable host addresses, before any additional provider reservations.

Why not subtract two for /31 and /32?

A /31 is commonly used for point-to-point links, with both addresses usable under RFC 3021. A /32 identifies one address. The ordinary subnet subtraction does not apply.

Does IPv6 have broadcast addresses?

No. IPv6 uses mechanisms such as multicast instead. The final address shown here is a mathematical boundary, not a broadcast address.

How do I divide a network into subnets?

Use the subnet splitter below with the existing CIDR and a longer prefix. If you only have start and end IPs, use the IP range calculator for exact CIDR coverage.