IPv6 Prefix Calculator
Break an IPv6 prefix into its network portion, available subnet count and address capacity.
About IPv6 Prefix Calculator
The network portion is produced by masking every 16-bit group down to the prefix length. Subnet count is the difference in prefix lengths as a power of two, and each subnet keeps 128 minus its own prefix bits for interfaces. IPv6 allocations are handed out as /48 or /56 blocks and the whole design depends on knowing how many /64s that yields before addresses are burned into DNS and firewall policy.
Formula
IPv6 Prefix
subnets = 2^(target − prefix); addresses per subnet = 2^(128 − target).
- prefix
- Length of the allocated prefix
- target
- Prefix length of each carved subnet
Worked example
With the default values below, IPv6 Prefix Calculator returns Network Prefix of 2001:db8:acad::/48. Change any input above and every figure here is recalculated in your browser.
Inputs used
- IPv6 address or prefix
- 2001:db8:acad::
- Prefix lengthaccepts 0–128 bits
- 48 bits
- Subnet size to carveaccepts 1–128 bits
- 64 bits
Results
- Network Prefix
- 2001:db8:acad::/48
- Subnets Available
- 65,536
- Host Bits per Subnet
- 64
- Addresses per Subnet
- 18,446,744,073,709,552,000
Step by step
- 1Values used
- 2IPv6 Prefix
- 3Network Prefix= 2001:db8:acad::/48
- 4Subnets Available= 65,536
- 5Host Bits per Subnet= 64
- 6Addresses per Subnet= 18,446,744,073,709,552,000
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is IPv6 Prefix calculated?
subnets = 2^(target − prefix); addresses per subnet = 2^(128 − target). The network portion is produced by masking every 16-bit group down to the prefix length. Subnet count is the difference in prefix lengths as a power of two, and each subnet keeps 128 minus its own prefix bits for interfaces.
Why does IPv6 Prefix matter?
IPv6 allocations are handed out as /48 or /56 blocks and the whole design depends on knowing how many /64s that yields before addresses are burned into DNS and firewall policy.
What values do I need to enter?
This calculator takes 3 inputs: IPv6 address or prefix, Prefix length, Subnet size to carve. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.