IPv6 CIDR Calculator
Enter an IPv6 prefix to get the first and last address of the block, both compressed and fully expanded, with the total address count and the number of /64 subnets.
- Runs in your browser
- Free to use
About this tool
IPv6 prefixes are allocated in large blocks: ISPs hand out /56 or /48 networks, and each LAN gets a /64. This calculator uses arbitrary-precision arithmetic in your browser to expand any prefix into its first and last address, the netmask, the address type, the exact number of addresses and how many /64 subnets fit inside, so you can plan an addressing scheme or document an allocation without a spreadsheet.
Results are shown in RFC 5952 compressed form and in fully expanded form, ready to paste into firewall rules or reverse-DNS zone files. The IPv4 CIDR Calculator covers the v4 side.
How to use it — quick steps
- 01
Enter the ipv6 cidr
Type or paste the ipv6 cidr in the field above, for example 2001:db8:abcd::/48.
- 02
Press "Calculate IPv6 subnet"
Press "Calculate IPv6 subnet" or Ctrl + Enter. The result appears instantly below the form.
- 03
Read the result
It appears in the dark panel under the form instantly. Every block has [copy] and other actions.
Key features of this tool
Nothing leaves your browser
The processing is plain JavaScript that runs on your device: the text you paste is never uploaded to our servers or to anyone else.
Instant results
Results appear the moment you press the button, even for long inputs, and every block has copy and download actions.
Works everywhere
No installation, no account and no limits: the tool works on desktop and mobile, in any modern browser, as often as you like.
Frequently asked questions
Why are the numbers so large?
IPv6 addresses are 128 bits long. A /64, the standard size for a single LAN, contains 18 quintillion addresses; a /48 contains 65,536 of those /64 networks.
What is the expanded notation?
The address written with all eight 16-bit groups and leading zeros, without the :: shortcut. Some tools and databases require this form.
What address types are detected?
Global unicast (2000::/3), unique local (fc00::/7), link-local (fe80::/10), multicast (ff00::/8) and loopback.