IPv6 Subnet Address Count
Understand how much address space each IPv6 subnet provides. Supply the CIDR prefix length (for example /64 or /56) and the calculator reveals the total count of usable addresses for capacity planning and allocation sizing.
CalcSimpler Examples
- Prefix /64 ⇒ 18,446,744,073,709,551,616 addresses
- Prefix /48 ⇒ 1,208,925,819,614,629,174,706,176 addresses
- Prefix /56 ⇒ 72,057,594,037,927,936 addresses
- Prefix /32 ⇒ 79,228,162,514,264,337,593,543,950,336 addresses
FAQ
Why are the numbers so large?
IPv6 uses 128-bit addresses, yielding vast address spaces.
Can prefix exceed 128?
No, valid prefixes range from 0 to 128.
Are reserved addresses included?
Yes, this counts all addresses in the range.
What happens if I enter a value outside 0–128?
The calculator automatically clamps the prefix to the valid range before computing the address count.
How can I convert the result to /64 subnets?
Divide the total address count by 18,446,744,073,709,551,616 to estimate how many /64 networks fit inside your allocation.
Additional Information
- IPv6 uses 128-bit addressing, so every reduction of the prefix by one bit doubles the number of available addresses.
- Enterprise LANs commonly receive /64 subnets to preserve autoconfiguration features.
- Regional Internet Registries often allocate /48 or shorter prefixes to organizations to enable subnetting flexibility.
- To estimate host capacity, subtract any reserved addresses required by your routing or security policies.
CalcSimpler