Enter an IPv4 address and choose a prefix length. Results update as you type. Everything runs locally in your browser, so nothing is sent to a server.
- network
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- usable
- —
- broadcast
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- hosts
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How to use the subnet calculator
Type an IPv4 address and choose a prefix length from /0 to /32. The network address, usable host range, broadcast address and host count update on every keystroke. The math uses 32-bit unsigned integers, so the results match what a router or ipcalc reports.
Reading the output
The network address is the first address in the block and cannot be assigned to a host. The broadcast address is the last address and also cannot be assigned. Usable hosts are everything in between, which is why a /24 has 254 usable addresses out of 256. A /31 and /32 are special cases used for point-to-point links and single hosts.
Common subnetting mistakes
An address inside a private range is not automatically reachable: the route, security group and host firewall still decide that. Do not size a subnet only for today's hosts either, because growing a block later usually means renumbering. Check the mask on both ends of a connection; a mismatched prefix is the usual cause of one-way reachability.