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IP subnet calculator

Calculate network address, broadcast, netmask and host range from CIDR notation.

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IP subnet calculator
Paste one or more IPv4 networks and this calculator expands each into the numbers that matter: network address, broadcast address, subnet mask in dotted and prefix notation, wildcard mask, the first and last usable host, the usable host count, and the address class with a private, public, loopback or link-local note. Three input forms work, one per line: CIDR like 192.168.1.0/24, an address with a mask like 10.0.0.0 255.255.0.0, or a bare IP that takes the default prefix set in the options.
It replaces the back-of-envelope binary arithmetic behind everyday network jobs: carving an office network into VLANs, sizing a DHCP scope, checking whether two machines actually share a subnet, or writing access lists — the wildcard mask is exactly what Cisco ACLs expect. Point-to-point /31 links follow RFC 3021 and report two usable addresses, and a /32 host route reports one. Turn on "Show binary" to see the network and mask in dotted binary — the fastest way to verify, or teach, exactly where the prefix boundary falls.
Your addressing plan is infrastructure information that should not leave your machine, and here it never does: every calculation runs locally in your browser, with nothing uploaded, logged or stored anywhere.
Paste a whole plan at once — each line becomes its own labeled block, invalid lines get a calm note without stopping the rest, and the tally under the output counts the subnets calculated as you type.
FAQ
Is my network plan uploaded anywhere?
No. Every calculation runs entirely in your browser and your addresses never leave your device — safe even for internal addressing plans.
What input formats are accepted?
One entry per line: CIDR notation like 192.168.1.0/24, an address followed by a mask like 10.0.0.0 255.255.0.0, or a bare IP, which takes the default prefix from the options.
How are /31 and /32 networks handled?
A /31 follows RFC 3021 for point-to-point links, so both addresses are usable hosts. A /32 is a single host route with exactly one address.
What is the wildcard mask for?
It is the bitwise inverse of the netmask — the form Cisco ACLs and OSPF network statements expect, so you can copy it straight into router configuration.