IPv6 Subnet Calculator (CIDR)
Expand and compress IPv6 addresses, find the network prefix, first/last address, address count, address type, reverse DNS zone and split a prefix into smaller subnets.
How to use the IPv6 Subnet Calculator
- Enter or select: IPv6 address / prefix.
- Fill in what you know of: Split into subnets of prefix length — leave the unknown empty.
- The results (Expanded address, Compressed address (RFC 5952), Network (prefix), First address, Last address, Addresses in prefix, Prefix length, Number of /64 subnets, Address type, Interface identifier (low 64 bits), Reverse DNS zone, Number of subnets after split, First subnets after split) are calculated instantly as you type.
- Use “Copy link” to share the calculation with the same input values.
Formula
- Network = address AND mask
- Addresses = 2^(128 − prefix)
- /64 subnets = 2^(64 − prefix)
About this tool
Handles zero compression (::), embedded IPv4 notation, and arbitrary-precision counts. A /64 is the standard subnet size for hosts (required for SLAAC).