IPv6 Subnet Calculator

Calculator

IPv6 address

You may paste “address/prefix” here too.

Base prefix length

Common choices: 48, 56, 64.

Display format

Affects network, range, and list output.

Planning method

Pick the style that matches your design task.

New prefix length

Must be ≥ base prefix and ≤ 128.

Requested subnets

New prefix uses ceiling log2(subnets).

Addresses per subnet

Size uses ceiling log2(addresses).

Subnets to list

Keeps the page responsive for large plans.

Example input	Base prefix	Target choice	What you should see
2001:db8:abcd:12::1	/64	New prefix /68	16 subnets, each with 2^60 addresses.
2001:db8:1234::	/48	64 subnets	New prefix /54 with 64 subnet ranges listed.
2001:db8:aa::	/56	Addresses per subnet = 2^64	Target prefix /64 (classic interface boundary).

These examples use documentation prefix ranges for safe testing.

Total addresses in a prefix: 2^(128 − prefix)
Subnet bits added: newPrefix − basePrefix
Available subnets: 2^(newPrefix − basePrefix)
Addresses per subnet: 2^(128 − newPrefix)
Network range: from subnet network (all host bits 0) to last address (all host bits 1)

IPv6 subnetting is bit-based. The prefix length fixes the network portion; remaining host bits define the address space inside each subnet.

For large allocations, list a small subset first, then increase the list count if needed.