IP subnet / CIDR calculator
Work out the network, broadcast, netmask, wildcard, host range and usable hosts from an IP and CIDR prefix.
How to use
Type an IPv4 address with its CIDR prefix — for example 192.168.1.10/24 — and the calculator instantly works out the network address, broadcast address, subnet mask, wildcard mask, the usable host range and the number of hosts. You can also paste an address and a dotted netmask (10.0.0.1 255.255.255.0) and it will derive the prefix for you.
Every value has a copy button, and the tool tells you whether the address falls in a private/reserved range (RFC 1918) or is publicly routable, plus its traditional class (A/B/C). It runs entirely in your browser, so you can use it offline and nothing you type is sent anywhere.
Common uses: planning how many subnets and hosts you need, double-checking a firewall or router rule, studying for a networking exam, or quickly confirming the broadcast address before configuring a device.
Examples
192.168.1.10/24 → network 192.168.1.0, broadcast 192.168.1.255, 254 usable hosts (192.168.1.1–192.168.1.254).
10.0.0.0/31 gives 2 usable addresses (RFC 3021) — ideal for router-to-router links.
8.8.8.8/32 represents one address, commonly used in ACLs and route statements.
Frequently asked questions
What's the difference between total and usable hosts?
Total addresses includes the network and broadcast addresses; usable hosts excludes them. For a /24 that's 256 total but 254 usable. For /31 and /32 the special RFC 3021 rules apply (2 and 1 usable).
Can I enter a netmask instead of a CIDR prefix?
Yes. Enter the IP and a dotted netmask separated by a space, e.g. 172.16.0.5 255.255.0.0, and the tool converts it to the equivalent /16 prefix.
How do I know if an address is private?
The tool flags RFC 1918 ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), loopback (127.x) and link-local (169.254.x) as private/reserved; everything else is shown as publicly routable.
Is my input sent to a server?
No. All the maths happens locally in your browser, so it works offline and keeps your addressing private.
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