webutilkit

IP Subnet Calculator

Calculate network address, broadcast address, and usable host range from CIDR notation.

How it works

The IP address and CIDR prefix are converted to 32-bit numbers. Applying the subnet mask to the address gives the network address; flipping the mask and combining it with the network address gives the broadcast address. Everything in between is the usable host range.

Reading CIDR notation

A /24 means the first 24 bits identify the network, leaving 8 bits (256 addresses) for hosts. A smaller number after the slash means a bigger network; a larger number means a smaller one — a /30 has only 4 addresses total.

Special cases at the edges

A /31 subnet has exactly 2 addresses and is commonly used for point-to-point links where both addresses are usable. A /32 identifies a single host, with no separate network or broadcast address at all.

Frequently asked questions

What does the /24 in an address like 192.168.1.0/24 mean?

It is the CIDR prefix length: the number of leading bits that identify the network, out of 32 total bits in an IPv4 address. A /24 leaves 8 bits for host addresses, giving 256 addresses in the subnet.

Why is usable host count 2 fewer than the total?

The first address in a subnet is reserved as the network address and the last as the broadcast address, so neither can be assigned to a device — except in /31 and /32 subnets, which are too small to have either.