This Subnet Calculator takes an IPv4 address and a CIDR prefix and works out everything else you'd otherwise need to calculate by hand: the network address, the broadcast address, the subnet netmask (both in dotted-decimal and binary form), and the total versus usable host counts for that subnet size. It's aimed at network admins, students studying for networking certifications, and anyone configuring a router or firewall who needs to double-check a subnet's boundaries.
Adjusting the CIDR prefix slider recalculates every value instantly, which makes it useful for exploring how subnet size trades off against host capacity — a smaller prefix number means a larger subnet with more usable hosts, and the calculator makes that relationship immediately visible instead of requiring manual binary math for every attempt.
How to Use Subnet Calculator
- Type an IPv4 address into the IP Address field (defaults to 192.168.1.1).
- Drag the CIDR Prefix slider or type a value directly into the number field beside it — the two stay in sync.
- Read the network address, broadcast address, netmask, and wildcard mask, which recalculate instantly as you type.
- Check the first/last usable IP and total/usable host counts for that subnet size.
- Check the IP class and binary netmask at the bottom of the results panel.
Features
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Network address, broadcast address, and netmask calculation
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Netmask shown in both dotted-decimal and binary
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Total and usable host counts for the subnet
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Live recalculation as you adjust the CIDR prefix
