IP Subnet Calculator

What is a subnet calculator?

A subnet calculator takes an IPv4 address and a network prefix and works out all the key details of the network it belongs to. It saves you from doing binary arithmetic by hand and is an everyday tool for network administrators planning, dividing or troubleshooting networks. Everything is computed locally in your browser.

How subnetting works

An IPv4 address is 32 bits, split into a network part and a host part. The CIDR prefix (for example /24) says how many leading bits identify the network, which fixes the subnet mask. From that, the calculator derives the network address (all host bits 0), the broadcast address (all host bits 1), the usable host range in between and the total number of addresses, which is 2 to the power of the remaining host bits.

How to use this calculator

Enter an IPv4 address such as 192.168.1.10, choose a prefix from /0 to /32, and press Calculate. You will see the network and broadcast addresses, the subnet and wildcard masks, the first and last usable hosts, the host count, the address class and whether the address is private or public.

Notes on special cases

Normally the network and broadcast addresses are reserved, so usable hosts equal the total minus two. A /31 is treated as a point-to-point link (2 usable addresses under RFC 3021) and a /32 represents a single host. Private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are for internal networks and are not routed on the public internet.