IPv6 Subnet Calculator
Free IPv6 subnet calculator and IPv6 CIDR calculator. Find the network prefix, IPv6 address range, prefix length, /64 subnet size, and compressed or expanded address format.
IPv6 CIDR
Use CIDR notation, for example 2001:db8::1/64. Zone IDs (after %) are ignored. IPv4-style tails like ::ffff:192.0.2.1 are supported.
Network (subnet) address
2001:db8::
Last address in range
2001:db8::ffff:ffff:ffff:ffff
Prefix length
/64
Host bits
64
Addresses in subnet
2^64 (64 host bits)
| Network (subnet) address | 2001:db8:: |
|---|---|
| Last address in range | 2001:db8::ffff:ffff:ffff:ffff |
| Prefix length | /64 |
| Host bits | 64 |
| Addresses in subnet | 2^64 (64 host bits) |
This IPv6 subnet calculator converts IPv6 CIDR prefixes into the network address, IPv6 address range, prefix details, and subnet size. Use it as an IPv6 CIDR calculator, IPv6 prefix calculator, or IPv6 range calculator when working with /48, /56, /64, /120, and /128 allocations. It supports compressed and expanded IPv6 notation, strips zone identifiers, and accepts IPv4-mapped tails such as ::ffff:192.0.2.1. Everything runs locally in your browser.
How to Use IPv6 Subnet Calculator
Enter IPv6 CIDR
Use address/prefix, for example 2001:db8::1/64. You may use :: compression or a full eight-group form. If your address includes an IPv4 tail (::ffff:x.x.x.x), the tool converts that tail into hexadecimal pieces before masking. This makes it useful as an IPv6 CIDR calculator for both modern and mixed-format inputs.
Choose display format
Enable “Show expanded notation” to see all eight 16-bit fields zero-padded. Turn it off for the shortest compressed form (longest run of zero hextets collapsed with ::).
Interpret “Addresses in subnet”
For smaller host portions, you will see an exact decimal count (with grouping). For very large subnets, the tool shows 2^n where n is the number of host bits—writing the full decimal for a /64 would not be practical in a UI. This is especially helpful for common searches such as “how many addresses are in a /64 subnet?”
Remember: no IPv4-style broadcast
IPv6 relies on multicast and Neighbor Discovery instead of broadcast. You will not see a “broadcast address” row here because it is not defined the same way as in IPv4.
Calculator Features
128-bit aware
Subnet math uses 128-bit semantics appropriate for IPv6.
Compressed or expanded
Switch between RFC 5952 compressed and fully expanded notation.
IPv4-mapped tails
Parse ::ffff dotted tails commonly seen in dual-stack environments.
Copy each value
One click per row to copy network, last address, and metadata.
Runs locally
No addresses are sent to a server; everything stays in the browser.
Prefix clarity
Shows prefix length, host bits, and IPv6 subnet size alongside the network.
Complete Function List
- IPv6 CIDR parsing (0–128 prefix):
- Network address after masking:
- IPv6 address range calculation:
- Last address in the subnet range:
- Host bit count:
- Subnet size (decimal or 2^n):
- IPv6 /64 and other common prefix checks:
- Expanded vs compressed output toggle:
- Zone ID stripping (%interface):
- Copy-friendly results table:
- Educational /0 warning:
Common Calculations & Examples
Example 1: Documentation prefix (/64)
Problem: You were given 2001:db8:abcd:ef01::/64 and want the network string.
Steps:
- Enter 2001:db8:abcd:ef01::1/64
- Read the Network row
Explanation: /64 is one of the most common IPv6 queries because it is the standard subnet size for many LAN deployments and provider recommendations.
Example 2: How many addresses are in a /64?
Problem: You need the subnet size for a /64 IPv6 network.
Steps:
- Enter any IPv6 address with /64
- Read the “Addresses in subnet” row
Explanation: This is a common long-tail search and the page answers it directly without forcing users to do exponent math themselves.
Example 3: Provider block planning (/48)
Problem: You want to inspect a /48 IPv6 allocation and confirm its network prefix.
Steps:
- Enter an address inside the block with /48
- Read the masked network address and host bits
Explanation: /48 is a frequent planning query for organizations and labs that subdivide larger IPv6 allocations.
Example 4: Small block (/120)
Problem: You need boundaries for 2001:db8::/120.
Steps:
- Enter any address inside the block with /120
- Inspect network and last address
Explanation: Large prefixes (many fixed bits) create small subnets—useful for loops or tight allocations.
Example 5: IPv4-mapped example
Problem: You see ::ffff:192.0.2.128/128 in logs.
Steps:
- Paste ::ffff:192.0.2.128/128 into the field
- Compare expanded vs compressed views
Explanation: IPv4-mapped IPv6 addresses embed an IPv4 address in the low 32 bits.