Expand and compress any IPv6 address, find the network and last address, count total addresses and /64 subnets, and identify the address type — instant as you type. The same engine that powers the Subnet Plus app, free on the web.
Browsers can't open raw network sockets — so live IPv6 lookups and path tracing only run on-device. Subnet Plus brings the whole toolkit to your iPhone, iPad & Mac, and syncs your saved subnets over iCloud. Free to download.
Common allocation sizes, how many /64 subnets each holds, and where they're used.
| Prefix | /64 subnets | Addresses (2^n) | Typical use |
|---|---|---|---|
| /32 | 4,294,967,296 | 2^96 | Regional registry (RIR) allocation to an ISP |
| /40 | 16,777,216 | 2^88 | Large ISP / enterprise block |
| /48 | 65,536 | 2^80 | Typical end-site / business allocation |
| /56 | 256 | 2^72 | Common home / small-site allocation |
| /60 | 16 | 2^68 | Small residential delegation |
| /64 | 1 | 2^64 | A single LAN / subnet (SLAAC standard) |
| /127 | — | 2 | Point-to-point link (RFC 6164) |
| /128 | — | 1 | Single host route |
Enter an IPv6 address with a prefix length, for example 2001:db8::/48. The calculator applies the prefix to find the network (first) address, the last address in the block, the expanded and compressed forms, the total number of addresses (2^(128 − prefix)), and the address type.
A /48 contains 65,536 /64 subnets (2^16) and a /56 contains 256 /64 subnets (2^8). In general the number of /64s in a prefix of length p is 2^(64 − p) for any p ≤ 64.
A /64 leaves 64 bits for the interface identifier, which is what SLAAC (stateless address autoconfiguration) and many other IPv6 mechanisms expect. Subnets longer than /64 break SLAAC, so /64 is the recommended size for a single LAN.
Expanded form writes all eight 16-bit groups with leading zeros, e.g. 2001:0db8:0000:0000:0000:0000:0000:0001. Compressed form removes leading zeros and replaces the longest run of zero groups with ::, e.g. 2001:db8::1. Both represent the same address.
Yes, it is completely free and runs entirely in your browser with no signup. For DNS lookup, ping, and traceroute, which need a real network device, download the free Subnet Plus app for iPhone, iPad, and Mac.
This free IPv6 subnet calculator works entirely in your browser — nothing is sent to a server. Enter any IPv6 address with a CIDR prefix to instantly see the network address, the expanded and compressed forms, the last address in the block, the total number of addresses, how many /64 subnets the prefix contains, and the address type (global unicast, unique local, link-local, multicast, loopback, or documentation).
The web tools cover address math: this IPv6 calculator plus the IPv4 subnet calculator, VLSM designer, and mask converter. The Subnet Plus app adds the tools that need a real device — DNS lookup, ping, and traceroute — plus iCloud sync, a saved library, history, and full offline use across iPhone, iPad, and Mac. It's been trusted by network engineers since 2013.