SubnetCalc
Calculate subnet

CIDR conversion

Convert CIDR to a subnet mask

Turn a prefix from /0 through /32 into its dotted-decimal mask, wildcard mask, block size, and usable-address interpretation.

Private browser calculation

Address, prefix, and host sizing

Stays on this page

Calculation mode

IPv4 address and prefix

Use a separate prefix or mask, or enter address/prefix and leave the second field empty.

A /31 result is blocked until you explicitly confirm its two endpoint semantics. Other prefixes ignore this choice.

Exact unsigned 32-bit arithmetic runs locally. This tool does not query, scan, locate, or test any address, and it does not configure a device.