Enter an IPv4 address with a prefix length in CIDR notation such as 192.168.1.0/24 and the calculator derives every part of the subnet: the dotted-decimal subnet mask, the network (base) address, the broadcast address, the first and last usable host, the total and usable host counts, and the inverse wildcard mask used in ACLs. The address is converted to a 32-bit integer and everything is computed with pure bitwise AND / OR / shift operations, the same math a router does.
Prefix lengths from /0 to /32 are supported. The /31 and /32 edge cases are handled correctly: a /32 describes a single host with no usable range, and a /31 point-to-point link exposes both addresses as usable per RFC 3021. Every result field has a one-click copy button, and nothing ever leaves your browser.