Kodura Subnet Calculator

A subnet calculator that answers before you finish typing.

Open it and the mask, wildcard and host count are already on screen. Drag the prefix and watch every value move with it. Type an address when you want the actual range — network, broadcast, first and last usable host.

SEE THE BOUNDARY Most calculators print the mask in binary as a wall of ones and zeros. What actually matters is where the network ends and the host portion begins, so this draws that boundary as a ruler of 32 bits, grouped into octets, and lets you drag it.

IPv6 DONE PROPERLY Compressed and expanded forms, embedded IPv4, zone identifiers, RFC 5952 canonical output. Address counts are exact — a /0 holds a 39-digit number, and this reports it rather than rounding. Prefixes report how many /64 subnets they contain, because that is the unit IPv6 is actually allocated in.

CORRECT AT THE EDGES /31 point-to-point links have no broadcast address and two usable hosts (RFC 3021). /32 is a single host. Plenty of calculators get these wrong. This one says so plainly.

FLEXIBLE INPUT Type a network, or paste whatever you already have: • CIDR notation — 10.0.0.0/8 • Address and mask — 192.168.1.10 255.255.255.0 • Wildcard masks — 10.1.1.0 0.0.0.255 • BSD ifconfig, including hex netmasks like 0xffffff00 • Linux ip addr output • Cisco running-config and show ip interface brief

SHOWS ITS WORKING When the prefix came from a subnet mask, a wildcard, or a hex netmask rather than plain CIDR, it says which — so you can see what it inferred instead of taking it on trust.

ALSO • Tap any address or mask to copy it • Binary view for masks and addresses • Classification — private, public, loopback, link-local, CGNAT, documentation • Legacy class A–E for coursework and exams • Light and dark, both designed rather than inverted

NO ACCOUNT, NO TRACKING No sign-up. No analytics on what you calculate. No tracking permission prompt, because the app does not track you. Ads are non-personalised.

Built by Kodura for network engineers, sysadmins, and anyone studying for CCNA or Network+.