IP Subnet Calculator

How to use the subnet calculator

1. Type an address with its prefix in IP address with prefix or mask: 192.168.1.10/24, 10.0.0.1 255.255.0.0, 172.16.5.4/255.255.240.0 or 2001:db8::1/48. A wildcard mask such as 0.0.0.255 is recognised too. Without a prefix, /24 (IPv4) or /64 (IPv6) is assumed and the tool says so.
2. Press Enter or click Calculate, or try one of the Examples:.
3. Read the Results, and click Copy to copy them all as text.
4. Under Subnetting, choose a Method, fill in Number of subnets or Hosts needed per subnet, and click Split.

What the results mean (IPv4)

• Network address: the first address of the block, with all host bits at 0. It identifies the subnet.
• Broadcast address: the last address, with all host bits at 1. Packets sent to it reach every host of the subnet.
• First usable host and Last usable host: the range you can assign to devices. Usable hosts is 2^(32 − prefix) − 2, because the network and broadcast addresses are reserved. A /31 is the exception: on point-to-point links both addresses are usable (RFC 3021), and a /32 is a single host.
• Subnet mask and Wildcard mask: the mask has 1s for the network bits (255.255.255.0 for /24). The wildcard is its inverse (0.0.0.255), as used in Cisco ACLs and OSPF.
• Address type: private ranges from RFC 1918 (10/8, 172.16/12, 192.168/16), the CGNAT range 100.64/10, loopback, link-local 169.254/16, documentation ranges, multicast and public addresses. Class (historic) gives the old A–E class, which no longer decides the mask since CIDR.
• Integer value, Hexadecimal and Reverse DNS (PTR) help with databases, firewalls and DNS zones.

The Binary view (network bits | host bits) section shows the address, the mask, the network and the broadcast address in binary, with the network bits highlighted: you can see exactly where the prefix cuts the address.

IPv6

For IPv6 the tool shows the Compressed form (RFC 5952: lowercase, leading zeros removed, the longest run of zero groups replaced by ::) and the Expanded form with all 32 hex digits, plus the network, last address and range. The Total addresses of a /64 is 2^64, about 18.4 quintillion. IPv6 has no broadcast, so every address in the block can be assigned. Typical sizes: /48 for a site, /56 for a home, /64 for one LAN segment.

Subnetting and VLSM

Equal subnets splits the block into at least the number you ask for, rounded up to a power of two: 3 subnets of a /24 become four /26 blocks of 62 hosts. VLSM (hosts per subnet) takes a list such as Sales: 50, IT: 20, Office: 10, sorts it from largest to smallest and gives each group the smallest block that fits its hosts plus the network and broadcast addresses, one after another. Largest-first keeps every block aligned on its own size, which is required for valid subnets. The summary shows how many addresses remain free for growth.