What is an IPv6 calculator?
An IPv6 calculator does the hex and binary work of IPv6 subnetting for you. Give it an address and a prefix length, such as /64, and it shows the network the address belongs to: where it starts, where it ends, how many addresses it holds and what kind of address it is.
It also writes the address in both forms, full and compressed, and splits it into the network part and the host part (the interface ID). That saves a lot of time, because IPv6 addresses are long and easy to misread.
How to use this calculator
Type the address in the first box, for example 2001:db8:acad:10:21a:2bff:fe3c:4d5e. Short forms with :: work too. If you paste an address with its prefix, like 2001:db8::/32, the prefix moves to the slider for you. If the address is not valid, the box turns red and tells you what to fix.
Drag the slider anywhere from 0 to 128. The badge next to it shows the prefix, like /64. A bigger number means a smaller network. Most LANs use /64.
The table follows every change. Network Address is the first address of the network, and First Address and Last Address give the whole range. Full IPv6 Address and Compressed Address show your address in both forms. Host Portion (Interface ID) is the part of the address that identifies the device, and Interface ID Type tells you if it looks like it was built from a MAC address.
Total Addresses and Number of /64 Networks show the size of the network. Address Type and Scope say what the address is for, for example global unicast, unique local, link-local or documentation. The last rows give the solicited-node multicast address and the reverse DNS names.
Copy puts the whole table on your clipboard as plain text. Download saves it as a CSV file that opens in Excel or Google Sheets. Both buttons are greyed out while the address has an error.
How the IPv6 subnet maths works
An IPv6 address is a 128-bit number. The prefix length says how many bits at the start are the network part. The rest are host bits. Every result comes from a few operations on those bits:
Unlike IPv4, there is no broadcast address, so the first and the last address of an IPv6 network can both be used. The first one is also the subnet-router anycast address, which routers answer to.
Worked example: 2001:db8:acad:10:21a:2bff:fe3c:4d5e/64
The prefix is /64, so the first 64 bits, 2001:0db8:acad:0010, are the network and the last 64 bits, 021a:2bff:fe3c:4d5e, are the interface ID. Setting all host bits to 0 gives the network address 2001:db8:acad:10::. Setting them all to 1 gives the last address 2001:db8:acad:10:ffff:ffff:ffff:ffff. The interface ID has ff:fe in the middle, which is the sign of EUI-64, and the MAC address inside it is 00:1A:2B:3C:4D:5E.
This table is built by the same code as the calculator above, so the two always match.
Common IPv6 prefix lengths
These are the sizes you will meet most often:
| Prefix | Total addresses | Number of /64 networks | Typical use |
|---|
IPv6 address types
| Block | Type | Meaning |
|---|---|---|
| 2000::/3 | Global unicast | Public addresses, routed on the internet |
| fc00::/7 | Unique local (ULA) | Private addresses, like 10.0.0.0/8 in IPv4 |
| fe80::/10 | Link-local | Works only on one link, never routed |
| ff00::/8 | Multicast | Group addresses, replace broadcast |
| ::1/128 | Loopback | This device |
| ::/128 | Unspecified | No address yet |
| 2001:db8::/32 | Documentation | Used in examples and manuals |
| ::ffff:0:0/96 | IPv4-mapped | An IPv4 address written as IPv6 |
When it helps
Use it to plan an IPv6 address plan, to check a prefix before you write a firewall rule or a route, to expand or shorten an address, to find the reverse DNS zone for a network, and to check your answers when you study for CCNA or Network+.
To split an IPv6 network into smaller subnets and see them as a map, use the IPv6 Visual Subnet Calculator. For IPv4, use the IPv4 Subnet Calculator.