IPv6 Subnet Calculator

IPv4 addresses — the familiar four-number format like 192.168.1.1 — gave the world around 4.3 billion unique addresses. That sounds like a lot, but the internet has essentially used them all up. IPv6 was created to solve this problem. Instead of 32 bits, IPv6 uses 128 bits, producing an address space so large it would take hundreds of years to explain how big it is in plain numbers.

IPv6 addresses look different from IPv4. Instead of four decimal numbers separated by dots, they use eight groups of four hexadecimal characters separated by colons — for example 2001:0db8:85a3:0000:0000:8a2e:0370:7334. To keep things manageable, long strings of zeros can be shortened using a double colon shortcut, making the same address read as 2001:db8:85a3::8a2e:370:7334.

Type or paste any valid IPv6 address into the IPv6 Address field. The calculator accepts both full expanded addresses and shortened compressed addresses — you do not need to tidy it up before entering.

1. 1Click the IPv6 Address field at the top of the calculator.
2. 2Type your address in either format:
   Full form: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
   Short form: 2001:db8:85a3::8a2e:370:7334
   Both are accepted and produce the same result.
3. 3If the address is invalid the field will show a red error message. Double check that you have used colons not dots, and that no group has more than 4 hexadecimal characters.

The prefix length works the same way as CIDR notation in IPv4 — it tells the calculator where the network ends and the device portion begins. Drag the slider anywhere from /0 to /128.

1. 1Drag the Prefix Length slider to the prefix you need. The badge on the right updates as you drag to show the current value.
2. 2Not sure what prefix to use? Here are the most common ones:
   /128 — a single specific device, like a loopback address
   /64 — the standard size for one LAN segment or VLAN
   /56 — a typical block an ISP assigns to a home customer
   /48 — a typical block assigned to a business or organisation
   /32 — a block assigned to an ISP or large provider
3. 3The results update automatically as you move the slider — no need to click Calculate for prefix changes.

The results table updates automatically as you type or move the slider. Here is what each row means in plain terms:

1. →Network Address — The address that identifies your network block, shown with its prefix. This is what you advertise to routers.
2. →Full IPv6 Address — Your original address written out completely with all 8 groups and all leading zeros restored — no shortcuts.
3. →Compressed Address — Your address in the shortest valid form using the double colon shortcut wherever possible.
4. →Network Prefix — The left-hand portion of the address that identifies the network. The bits after your prefix length are zeroed out.
5. →Host Portion (Interface ID) — The right-hand portion that identifies the specific device. The bits before your prefix length are zeroed out.
6. →First Address / Last Address — The very first and last addresses in your network block. Unlike IPv4 there is no separate broadcast address in IPv6 — the last address is usable.
7. →Total Addresses — The total number of addresses in your block. For a /64 this is 2⁶⁴ — over 18 quintillion addresses.
8. →Address Type — Whether this is a Unicast (one device), Multicast (group of devices), or special address such as Loopback or Unspecified.
9. →Scope — How far this address can travel. Global means it is routable across the public internet. Link-Local means it only works on the directly connected network segment and never leaves it.
10. →Number of /64 Networks — How many standard /64 sized networks fit inside your block. A /48 for example contains 65,536 individual /64 networks.

Example — calculating 2001:0db8:85a3::8a2e:0370:7334 with a /64 prefix

The Address Type and Scope rows in the results tell you what kind of address you have entered and where it can be used.

IPv6 is the newer version of the Internet Protocol designed to replace IPv4. IPv4 uses 32-bit addresses giving around 4.3 billion possible addresses — a number the world has essentially run out of. IPv6 uses 128-bit addresses, which produces a number so astronomically large that every device on earth could have billions of its own addresses and we would still barely scratch the surface. It was created to make sure the internet can keep growing for centuries without ever running out of address space.

An IPv6 address is made up of 8 groups of 4 hexadecimal characters separated by colons — for example 2001:0db8:85a3:0000:0000:8a2e:0370:7334. To make addresses shorter and easier to read, leading zeros in each group can be dropped and one consecutive run of all-zero groups can be replaced with a double colon (::). So the example above becomes 2001:db8:85a3::8a2e:370:7334. Both write exactly the same address — just one is shorter.

An expanded address shows all 8 groups with all 4 characters each — nothing is hidden or shortened. A compressed address removes leading zeros from each group and replaces the longest run of consecutive all-zero groups with ::. For example 2001:0db8:0000:0000:0000:0000:0000:0001 compresses to 2001:db8::1. Both are the same address. Some equipment requires the full expanded form while others accept either — the calculator shows you both so you always have the right format ready.

The prefix length works exactly like CIDR notation in IPv4. It is written as a slash followed by a number from 0 to 128 — for example /64. The number tells you how many of the 128 bits identify the network, and the remaining bits identify the individual device. The /64 is the standard prefix for a single network segment — most home and office networks use /64 for every individual subnet, no matter how few devices are on it. ISPs typically hand out /48 or /56 blocks to customers, which are then divided into /64s internally.

A /64 leaves 64 bits for the device portion of the address. Two to the power of 64 is 18,446,744,073,709,551,616 — over 18 quintillion addresses in a single /64 subnet. This is completely intentional. In IPv6 the idea of carefully rationing addresses the way we did in IPv4 is gone. Every network segment gets a /64 and devices can automatically generate their own address within it without any manual configuration or a DHCP server. The abundance of space is a feature, not an accident.

No. IPv6 does not have a broadcast address. In IPv4 the last address of every subnet was reserved for broadcast — sending one packet to all devices on the network at once. IPv6 replaces broadcast entirely with Multicast, which is more efficient because packets are only sent to devices that have specifically joined a multicast group rather than flooding every device on the segment. This means in IPv6 the last address of any block is fully usable and can be assigned to a device.

Global Unicast addresses (starting with 2000::/3) are public internet addresses — they are routable anywhere in the world, just like a public IPv4 address. Link-Local addresses (starting with fe80::/10) are automatically assigned to every network interface and only work on the directly connected segment — they never cross a router and are used for things like automatic address discovery. Unique Local addresses (starting with fc00::/7) are the IPv6 equivalent of private IPv4 ranges like 192.168.x.x — they work internally but are not routed on the public internet.

This field tells you how many standard /64 sized network segments fit inside the block you have defined with your prefix length. For example a /48 block contains 65,536 individual /64 networks — enough for a large organisation to give every floor of every building its own /64 without ever running short. A /56 contains 256 /64 networks — typical for a home broadband customer. If your prefix is already /64 the answer is 1. If your prefix is larger than /64 — meaning a smaller block like /96 or /128 — this field shows Not Applicable because the block is too small to contain even a single /64.