IPv6 addresses are 128 bits of hexadecimal that humans were never meant to read unaided. The Gizmo 421 IPv6 Subnet Calculator expands and compresses any address, then works out the network range for any prefix — first address, last address, and exactly how many addresses the block contains.
Paste an address like 2001:db8::/32 and get the full 8-group expansion and the RFC 5952 compressed form, plus the network block: first and last address in the range (both formats) and the exact address count — even when that count is 2 to the 64th power. The parsing and math run on JavaScript’s BigInt, so nothing is lost to floating-point rounding on numbers this size.
Reading an IPv6 address
Eight groups of four hex digits, separated by colons — 128 bits. Leading zeros drop from each group, one run of consecutive zero groups collapses into a double colon, and that is the compressed form everyone actually types. The prefix works like IPv4’s CIDR notation: /64 means the first 64 bits are the network, and a standard /64 subnet contains 2 to the 64th addresses — more than the entire IPv4 internet squared.
Common questions
Why did my address not compress? Per RFC 5952, a single zero group stays written out — only runs of two or more collapse into ::. Can I enter IPv4? No — this calculator is pure IPv6; use the IPv4 Subnet Calculator for dot-quad math. What prefix should I use? /64 is the standard LAN size; ISPs typically delegate a /48 or /56 to a site, and /127s are common for router-to-router links.