IP Subnet Calculator

What is IP Subnetting?

IP subnetting divides a network into smaller sub-networks (subnets) using a subnet mask or CIDR (Classless Inter-Domain Routing) prefix. CIDR notation combines the IP address and prefix length — for example, 192.168.1.0/24 means the first 24 bits are the network portion and the remaining 8 bits identify individual hosts. The subnet mask (e.g. 255.255.255.0) is the dotted-decimal equivalent. Subnetting is essential for network design, IP address management, routing, and firewall configuration. Key values include: network address (first address in the range), broadcast address (last address, sent to all hosts), and the usable host range in between.

How to Use the IP Subnet Calculator

Type an IP address with CIDR prefix (e.g. 192.168.1.1/24) or with a subnet mask (e.g. 192.168.1.1/255.255.255.0).
Results appear instantly: network address, broadcast, first/last host, usable host count, masks, IP class, and type.
The binary visualization shows which bits are network bits (blue) and which are host bits (grey).
Click any of the example buttons to load a common subnet configuration.
Supports /0 through /32, including /31 point-to-point links and /32 host routes.

Keywords: IP subnet calculator, CIDR calculator, subnet mask calculator, network address calculator, IP subnetting, broadcast address, host range calculator, CIDR notation