IPv6 Subnet Calculator
Calculate IPv6 subnets, address ranges, and network addresses instantly
Calculation Results
Enter an IPv6 address and prefix length to see results.
Common IPv6 Prefix Reference
| Prefix | Subnet Mask | Addresses | Use Case |
|---|---|---|---|
| /32 | ffff:ffff:: | 296 | ISP / RIR allocation |
| /48 | ffff:ffff:ffff:: | 280 | Site allocation |
| /56 | ffff:ffff:ffff:ff00:: | 272 | Large LANs |
| /64 | ffff:ffff:ffff:ffff:: | 264 | Standard subnet |
| /96 | ffff:ffff:ffff:ffff:ffff:ffff:: | 232 | IPv4-mapped |
| /112 | ffff:ffff:ffff:ffff:ffff:ffff:ffff:0 | 216 | Point-to-point |
| /127 | ffff:ffff:ffff:ffff:ffff:ffff:ffff:fffe | 2 | Inter-router links (RFC 6164) |
| /128 | ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff | 1 | Single host |
How to use the IPv6 subnet calculator
- Enter an IPv6 address in full or compressed form, such as
2001:db8:85a3::8a2e:370:7334. - Enter the prefix length, with or without a slash (
64or/64). - Results appear instantly. Save them to your history, export to CSV, or copy the page URL to share the calculation.
Understanding your results
- Expanded address — all eight 16-bit groups written out with leading zeros.
- Subnet mask — the prefix length written as an IPv6 mask.
- Network address — the first address in the prefix, shown in compressed form with its prefix length.
- Last address — the final address in the prefix. IPv6 has no broadcast address, so every address can be used.
- Number of addresses — the total size of the prefix.
- Number of /64 subnets — how many standard LAN subnets fit inside the prefix.
How IPv6 prefixes work
An IPv6 address is 128 bits long, written as eight groups of four hexadecimal digits. The prefix length tells you how many leading bits identify the network. Each additional bit halves the size of the prefix; each four bits (one hex digit) divides it by 16.
A typical plan gives each site a /48, carves out /56 or /60 blocks for buildings or functions, and assigns a /64 to each individual network segment. Because the boundaries fall on hex digits, well-planned IPv6 addresses are easy to read at a glance.
Common IPv6 prefix sizes
- /32 — a typical allocation to an ISP or large organization from a regional internet registry.
- /48 — a site allocation: 65,536 /64 subnets.
- /56 — common for small sites and residential service: 256 /64 subnets.
- /64 — a single LAN segment; required for SLAAC.
- /127 — point-to-point links between routers (RFC 6164).
- /128 — a single address, such as a loopback or host route.
Running both protocols? Our article on managing dual-stack IPv4 and IPv6 environments and the IPv6 adoption guide cover planning a transition. You can also lay out IPv4 and IPv6 subnets side by side in the free Network Planner.
Frequently Asked Questions
How many addresses are in an IPv6 /64?
A /64 contains 2^64 addresses — 18,446,744,073,709,551,616. That is why /64 is the standard size for a single IPv6 subnet: you will never run out of host addresses inside it.
Why is /64 the standard IPv6 subnet size?
IPv6 splits an address into a 64-bit network prefix and a 64-bit interface identifier. Stateless address autoconfiguration (SLAAC) and many other IPv6 features expect a /64, so LAN segments should almost always use a /64 even when they have only a handful of devices.
How many /64 subnets are in a /48?
A /48 contains 65,536 /64 subnets (2^16). A /56 contains 256 /64 subnets, and a /60 contains 16. The calculator shows the number of /64 subnets for any prefix of /64 or shorter.
How do you shorten (compress) an IPv6 address?
Remove leading zeros in each 16-bit group, then replace the longest run of all-zero groups with a double colon (::). The double colon can only appear once. For example, 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1. The calculator shows both the compressed and fully expanded forms.
What IPv6 prefix should my organization request?
Sites commonly receive a /48, which provides 65,536 /64 subnets. Smaller sites and residential connections often receive a /56 (256 subnets). Plan your allocation so each site, building, or function gets its own block that can grow over time.
What is a unique local address (ULA)?
Unique local addresses use the fc00::/7 range (in practice fd00::/8) and are the IPv6 equivalent of private IPv4 space. They are routable within your organization but not on the public internet. The calculator identifies ULA, link-local, global unicast, multicast, and other address types.
Is this IPv6 calculator free?
Yes. The IPv6 Subnet Calculator is free, requires no signup, and runs entirely in your browser. To manage IPv4 and IPv6 subnets together for your whole team, you can create a free Subnet24 account.
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