How this calculator works
Enter an IPv4 or IPv6 address with a prefix length, such as 192.168.10.37/26 or 2001:db8:1200::/40. The calculator applies the prefix as a mask and works out the network the address belongs to. Everything runs in your browser; nothing is sent anywhere.
How to read the results (IPv4)
- Network address is the first address in the block (all host bits zero). It identifies the subnet and isn't assigned to a host.
- Broadcast address is the last address (all host bits one). It isn't assigned to a host either.
- Usable hosts is the block size minus those two addresses. A /26 has 64 addresses and 62 usable hosts.
- Subnet mask and wildcard mask express the same prefix in dotted form. Firewalls and Cisco ACLs often want the wildcard (
0.0.0.63for a /26). - /31 and /32 are special: a /31 has two usable addresses for point-to-point links (RFC 3021), and a /32 is a single host.
How to read the results (IPv6)
IPv6 has no broadcast address, so every address in the block is usable. Subnets for hosts are normally /64, because stateless address autoconfiguration (SLAAC) needs 64 bits for the interface identifier. Sites typically receive a /48 or /56 to divide into /64s. A /48 contains 65,536 /64 subnets.
Common questions
Do two addresses share a subnet? Enter each with the same prefix. If the network addresses match, they're in the same subnet.
Which addresses are private? IPv4 private ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918). Shared carrier-grade NAT space is 100.64.0.0/10. IPv6 unique local addresses use fc00::/7, in practice fd00::/8.
Updated 26 October 2026