IPv6 Subnet Calculator
IPv6 subnet calculator — paste an IPv6 address and prefix to get the fully expanded and compressed forms, the network address, the first and last addresses in the block, and the total number of addresses. Runs entirely in your browser. No queries leave your device.
IPv6 Subnet Calculator
How to Use the IPv6 Subnet Calculator
Paste an address
Enter any IPv6 address, compressed or full.
Set the prefix
Type the prefix length from 0 to 128.
Read the block
See the network, first/last addresses and total count.
Copy forms
Use the compressed or expanded form wherever you need it.
Making Sense of 128-Bit Addresses
IPv6 was designed to solve the one problem IPv4 could never escape: running out of addresses. Where IPv4 uses 32 bits and offers roughly four billion addresses, IPv6 uses 128 bits and offers around 3.4 × 10³⁸ — a number so large it is effectively inexhaustible. The cost of that abundance is readability. A full IPv6 address is eight groups of four hexadecimal digits, and working with them by hand is error-prone. This calculator removes the guesswork: paste an address and a prefix, and it shows you the network, the first and last addresses, the total size of the block, and both the compressed and fully expanded forms side by side.
Two notation rules make IPv6 manageable, and the tool applies both exactly as the standard requires. First, leading zeros within each four-digit group may be dropped, so 0db8 becomes db8 and 0000 becomes 0. Second, the single longest run of consecutive all-zero groups may be replaced by a double colon — but only once per address, because allowing it twice would make the address ambiguous. Together these turn 2001:0db8:0000:0000:0000:0000:0000:0001 into the far friendlier 2001:db8::1. Seeing both forms together is genuinely useful when you are checking a configuration or hunting for a typo in a long address.
The prefix length works just as it does in IPv4 CIDR notation: it states how many leading bits identify the network. A /64 — the standard size for a single LAN — fixes 64 bits and leaves 64 for hosts, which is why even one ordinary subnet contains over eighteen quintillion addresses. Internet providers typically delegate larger blocks such as /56 or /48 to a site, each of which can be carved into many /64 subnets. Because the counts are astronomically large, the tool expresses them as powers of two rather than unwieldy decimals. Note too that IPv6 has no broadcast address — that job belongs to multicast — so the calculator reports a first-and-last range and a count rather than the network-and-broadcast pair familiar from IPv4. Everything is computed locally with big-integer arithmetic, so none of your addressing details ever leave your browser.
A single IPv6 /64 subnet holds more addresses than the entire IPv4 internet, squared — abundance is the whole point.
10 Facts About IPv6
IPv6 uses 128-bit addresses — IPv4 used just 32.
That’s about 3.4 × 10³⁸ possible addresses.
A single /64 holds 18 quintillion addresses.
Leading zeros in each group can be dropped.
One run of zero-groups can compress to :: — only once.
A home connection is often delegated a /56 or /48.
IPv6 has no broadcast address — it uses multicast.
::1 is the IPv6 loopback, like 127.0.0.1.
Link-local addresses start with fe80::.
This calculator runs in your browser — nothing is uploaded.
Frequently Asked Questions
- You enter an IPv6 address and a prefix length (the number after the slash, from 0 to 128). The tool expands the address to its full 8-group form, produces the shortest valid compressed form, then applies the prefix to find the network address, the first and last addresses in the block, and how many addresses the block contains. All of it happens locally in your browser.
- The prefix length states how many of the 128 bits identify the network, leaving the rest for hosts. A /64, the most common prefix for a single LAN, fixes the first 64 bits and leaves 64 bits — about 18 quintillion addresses — for devices. The larger the prefix number, the smaller the block.
- The expanded form writes all eight 16-bit groups in full, such as 2001:0db8:0000:0000:0000:0000:0000:0001. The compressed form drops leading zeros in each group and replaces the longest single run of all-zero groups with a double colon, giving 2001:db8::1. Both refer to exactly the same address; compression is just for readability.
- The double colon means “fill with as many zero groups as needed to reach eight groups total.” If it appeared twice, the address would be ambiguous — there would be no way to know how many zero groups belong to each gap. The standard therefore allows it only once per address, and this tool follows that rule.
- No. Unlike IPv4, IPv6 has no broadcast address; the role is handled by multicast and the all-nodes group instead. That is why this calculator reports a first and last address and a total count, rather than a network-and-broadcast pair the way an IPv4 subnet calculator does.
- It varies, but home and small-business connections are commonly delegated a /64, /60, /56 or /48. A /64 is a single subnet, while a /56 or /48 lets you create many /64 subnets behind your router. Enter the prefix your provider assigned to see exactly how large that delegation is.
- Because IPv6 blocks are so large that the exact decimal numbers would be unwieldy — a /64 holds 2⁶⁴ addresses, which is over 18 followed by eighteen digits. Expressing the count as a power of two (and an approximate power of ten) keeps it readable while still being precise.
- Yes. Network engineers use it to confirm where one subnet ends and the next begins, to check that addresses fall inside an allocation, and to document the first and last addresses of a block. Because it shows both compressed and expanded forms, it is also handy for spotting typos in long IPv6 addresses.
- No. The entire calculation runs in JavaScript on your device using big-integer maths. Nothing you type is transmitted, logged or stored, which makes the tool safe to use with internal or sensitive addressing information.
- Completely free, with no account or limit. It works offline once the page has loaded and collects no data.
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