subnet calculator

Take 2 to the power of (32 minus the prefix) and subtract 2 for the network and broadcast addresses. A /24 has 254 usable hosts, a /26 has 62 and a /30 has 2. The cheat sheet above lists every prefix from /16 to /32.

They describe the same thing. CIDR writes the number of network bits after a slash (/24); the subnet mask writes the same bits as four numbers (255.255.255.0). The calculator accepts either.

It is the inverse of the subnet mask (0.0.0.255 for a /24). Cisco ACLs and OSPF network statements use wildcard masks, which is why the calculator shows it next to the mask.

RFC 3021 lets point-to-point links use a /31 with no network or broadcast address, so both addresses are usable. That saves half the addresses compared with the old /30 habit. A /32 is a single host, often used for loopbacks.

Variable Length Subnet Masking gives each segment a subnet sized to its host count instead of one fixed size. The planner sorts your requests from largest to smallest and places each one on its own boundary, so nothing overlaps and gaps stay as small as possible.

A /48 holds 65,536 /64 subnets and a /56 holds 256. Use the IPv6 tab and choose which subnet size to count; it also shows the full expanded address and the ip6.arpa reverse zone.

No. Every calculation runs in your browser. Nothing you type is sent to a server, which makes it safe to use with internal addressing plans.