When you’d reach for this
IPv6 looks harder than it is, and most of the difficulty is just reading the address. The two jobs here are compression (turning a full 32-hex-digit address into its shortest legal form, and back) and prefixing (finding the network a /48 or /64 defines and how many smaller blocks fit inside). The calculator does both so you can check your own working: the method is in the IPv6 addressing lesson.
The prefixes you plan with
| Prefix | What it is | Contains |
|---|---|---|
/32 |
A typical allocation to an ISP | 65,536 × /48 |
/48 |
A site / organisation | 65,536 × /64 |
/56 |
A common home allocation | 256 × /64 |
/64 |
One LAN: the standard subnet | 264 addresses |
/127 |
Router-to-router link (RFC 6164) | 2 addresses |
/128 |
A single host route | 1 address |
Address types it recognises
| Range | Type | Meaning |
|---|---|---|
2000::/3 |
Global unicast | The routable public internet |
2001:db8::/32 |
Documentation | Reserved for examples: safe to publish |
fc00::/7 |
Unique local | Private addressing (IPv6’s RFC 1918) |
fe80::/10 |
Link-local | Valid on one link only, never routed |
ff00::/8 |
Multicast | One-to-many; IPv6 has no broadcast |
::1/128 |
Loopback | The host itself |
Learn the addressing behind it
This tool pairs with IPv6 addressing, and the IPv4 Subnet Calculator is its twin for the 32-bit world.
Frequently asked questions
How do you compress an IPv6 address?
Drop the leading zeros in each group, then replace the single longest run of all-zero groups with ::. So 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1. The :: may appear only once; if two zero runs are the same length, compress the first (RFC 5952).
What is a /64 and why is it the standard subnet?
A /64 uses the first 64 bits as the network and the last 64 as the interface identifier. It is standard for a LAN because SLAAC, the way hosts auto-build their own address, assumes 64 host bits. One /64 holds 264 addresses: about 18 quintillion.
How many /64 subnets are in a /48?
65,536. Going from /48 to /64 adds 16 network bits, and 216 = 65,536.
Does the calculator send my address anywhere?
No. Every step is big-integer math in your browser: no server call, no logging, works offline.