IPv6 Subnet Calculator
Explore IPv6 prefix sizes, subnet counts, and address space — and expand compressed addresses.
Your details
Subnetting
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Network prefix
2001:db8:85a3::0/64
1.845e+19 addresses in this prefix
Includes your inputs, the full breakdown, and every row of the table.
Address type
Documentation (2001:db8::/32)
Host bits
64
Subnets at /64
1
Addresses per subnet
1.845e+19
- Expanded address
- 2001:0db8:85a3:0000:0000:8a2e:0370:7334
- Compressed
- 2001:db8:85a3:0:0:8a2e:370:7334
- Prefix length
- /64
- Network prefix
- 2001:0db8:85a3:0000:0000:0000:0000:0000/64
- Total addresses
- 1.8447e+19
- Subnets when split into /64
- 1
| Prefix | Typical use | /64 subnets available |
|---|---|---|
| /32 | Regional registry allocation to an ISP | 4,294,967,296 |
| /48 | Site allocation for an organisation | 65,536 |
| /56 | Common residential allocation | 256 |
| /60 | Small residential allocation | 16 |
| /64 | Standard single subnet (SLAAC requires this) | 1 |
| /127 | Point-to-point link (RFC 6164) | — |
| /128 | Single host | — |
What this means
- IPv6 subnets are almost always /64. SLAAC address autoconfiguration requires exactly 64 host bits, so going smaller breaks stateless configuration.
- There is no broadcast address in IPv6 and no need to reserve a network address, so every address in a subnet is usable in principle.
- Leading zeros in each group can be dropped, and one run of all-zero groups can be replaced with :: — but only one run per address.
How the ipv6 subnet calculation works
IPv6 addresses are 128 bits written as eight groups of four hexadecimal digits. Two compression rules keep them readable: leading zeros within a group can be omitted, and a single run of consecutive all-zero groups can be replaced with a double colon.
Subnetting works the same way as IPv4 but with vastly more room. A /64 — the standard subnet size — contains 18.4 quintillion addresses, which is more than the entire IPv4 internet squared. The point is not to conserve addresses but to make routing and autoconfiguration simple.
Frequently asked questions
Why is /64 the standard IPv6 subnet size?
SLAAC generates the host portion of an address from a 64-bit interface identifier. Using anything other than /64 on a LAN breaks stateless autoconfiguration.
What does :: mean in an IPv6 address?
It replaces one or more consecutive groups of zeros. It can appear only once in an address, since more than one occurrence would make the expansion ambiguous.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.