Subnet Calculator

A subnet calculator takes an IP address and a subnet mask (or CIDR prefix) and instantly works out everything you need to know about that network: the network address, broadcast address, the range of usable host IPs, and how many devices can fit in the subnet. Instead of converting binary by hand, you type an address like 192.168.1.10/24 and read the results.

Subnetting splits one large network into smaller, isolated networks. It keeps broadcast traffic contained, makes IP space easier to manage, and is a foundational skill for network certifications like CCNA, Network+, and cloud networking on AWS, Azure, and Google Cloud.

CIDR (Classless Inter-Domain Routing) notation is the modern, compact way to write a network. The number after the slash — like the /24 in 10.0.0.0/24 — tells you how many of the 32 bits in an IPv4 address belong to the network. The remaining bits identify hosts. A larger prefix means a smaller network: a /24 holds 254 usable hosts, while a /16 holds 65,534.

This CIDR calculator converts between CIDR prefixes, dotted-decimal subnet masks (like 255.255.255.0), and wildcard masks automatically — so you never have to memorize the conversion table (though we include one below for quick reference).