🛰️ IPv6 Subnet Calculator
Paste any IPv6 address with a prefix and get its canonical compressed form, full expanded form, the network range, and how many addresses and /64 subnets it contains.
| Canonical (RFC 5952) | 2001:db8:abcd:12::1 |
|---|---|
| Fully expanded | 2001:0db8:abcd:0012:0000:0000:0000:0001 |
| Network prefix | 2001:db8:abcd:12::/64 |
| First address | 2001:0db8:abcd:0012:0000:0000:0000:0000 |
| Last address | 2001:0db8:abcd:0012:ffff:ffff:ffff:ffff |
| Total addresses | 18,446,744,073,709,551,616 (2^64) |
| Contains /64 subnets | this is one /64 (one LAN segment) |
/48 — typical site allocation: 65,536 LANs
/56 — typical home delegation: 256 LANs
/64 — one LAN segment, always
Exact 128-bit arithmetic (BigInt), entirely in your browser.
How the ipv6 subnet calculator works
IPv6 addresses are 128 bits written as eight groups of hex. The calculator parses any valid form (including :: compression and embedded IPv4 tails), computes the network range for your prefix with exact 128-bit arithmetic, and shows both the RFC 5952 canonical compressed form and the fully expanded form. Because IPv6 subnetting is about counting subnets rather than hosts — a standard LAN is always a /64 — it also tells you how many /64s fit in your allocation: a /56 holds 256 of them, a /48 holds 65,536. With IPv6 now carrying more than half of Google’s user traffic, dual-stack addressing plans are routine work rather than a future project.
The habit to unlearn from IPv4: conserving addresses. An ISP handing you a /56 is giving you 256 whole LANs, each with 18 quintillion addresses — the design intent is one /64 per network segment, no matter how few devices it has. Subnet on nibble boundaries (multiples of 4 bits) where possible; it keeps the hex readable.
Frequently asked questions
How many addresses are in a /64?
2^64 — 18,446,744,073,709,551,616 addresses. It is the standard size for a single network segment; SLAAC address autoconfiguration requires exactly 64 host bits.
How many /64 subnets are in a /48 or /56?
A /48 contains 65,536 /64s; a /56 contains 256. Those are the two most common delegated-prefix sizes for sites and home connections respectively.
What is the canonical (RFC 5952) form?
Lowercase hex, leading zeros dropped in each group, and the longest run of two or more zero groups compressed to :: (leftmost run if tied). It exists so an address always has one comparable text form.
Why should I subnet on nibble boundaries?
Each hex digit is 4 bits, so prefixes at multiples of 4 (/48, /52, /56, /60, /64) align with whole hex digits — subnets then differ by one visible character, which makes plans much easier to read and delegate in DNS.
Does the math really use 128 bits?
Yes — the calculator uses arbitrary-precision integers (BigInt), not floating point, so every bit of the 128-bit address space is exact.