Working out a subnet by hand takes practice, and even experienced network engineers double-check their maths before pushing a configuration live. This calculator does the binary conversion for you: enter an IP address and a CIDR prefix or subnet mask, and it returns the network address, broadcast address, usable host range, and number of available hosts in a fraction of a second. It runs entirely in your browser — nothing you type is sent to a server.
How to use the subnet calculator
- Enter an IPv4 address, for example 192.168.1.0.
- Enter the subnet mask or CIDR prefix, for example /24 or 255.255.255.0.
- Press calculate. You'll instantly see the network ID, broadcast address, first and last usable host, and total number of hosts.
Why subnetting still matters
Subnetting exists to solve a simple problem: a single flat network doesn't scale. As soon as you have more than a handful of devices, you need a way to group them logically, control broadcast traffic, and apply security policy at a boundary. This is also one of the most heavily tested skills on the CCNA and CompTIA Network+ exams, precisely because it's foundational. If you can't subnet confidently, VLANs, ACLs, and routing protocols become much harder to reason about.
Worked example
Take 192.168.10.0/26. A /26 mask borrows two extra bits from the host portion, giving you 4 subnets of 64 addresses each (62 usable, once you subtract the network and broadcast addresses). The first subnet runs from 192.168.10.0 to 192.168.10.63, with 192.168.10.1–192.168.10.62 usable for hosts.
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