Subnet Calculator

An IP address has two parts: the network it belongs to, and the host within that network. The prefix length says where the split falls. In 192.168.1.10/24 the first 24 bits, 192.168.1, name the network, and the last 8 bits name the host.

Every address that starts with the same network bits is in the same subnet and is reached directly. Anything else is reached through a router, usually the default gateway.

• Type an address with its prefix, as 192.168.1.10/24, or with its netmask, as 192.168.1.10 255.255.255.0. IPv6 works the same way: 2001:db8::1/64.
• The result appears as you type: the network, the addresses hosts can use, the broadcast address, the masks, and the kind of address block according to IANA.
• Is an address in this subnet? takes a second address and says whether the two are on the same network, the first question when two devices cannot reach each other.
• A click on a value selects all of it, ready to copy. The address bar follows what you type, so a result can be shared or bookmarked as a link.

• In IPv4 the first address of a subnet names the network and the last is its broadcast address, so neither can be given to a host. A /31 and a /32 are the exceptions: a point-to-point link and a single address.
• IPv6 has no broadcast address. A /64 is the usual size of one IPv6 network, because address autoconfiguration (SLAAC) expects it.
• A netmask is one unbroken run of ones followed by zeros. 0.0.0.255 is a wildcard mask, the form access lists use, and the page says so rather than guessing.
• A number with a leading zero, such as 010, is refused. Some systems read it as octal, where 010 is 8, so the same text would name two different addresses.
• The address type comes from the IANA special-purpose address registries, as published on 13 September 2026.