IPv6 Subnet Calculator
Calculate prefix details and address counts.
IPv6 Subnet Calculator: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
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How IPv6 Subnet Calculator Works?
This tool works by applying the prefix length to a 128-bit address and returning the network prefix, address count, and number of /64 subnets inside the block.
Enter an address and prefix
Type a value such as
2001:db8:acad:1234::abcd/56.Compute the network prefix
The first 56 bits stay and the rest become 0:
2001:db8:acad:1200::/56.Count the addresses
2^(128 − 56) = 2^72 addresses.
Count the /64 subnets
2^(64 − 56) = 256 standard LAN subnets fit inside the /56.
IPv6 Subnet Calculator Formula
The formula is Network = IP AND Mask, Addresses = 2^(128 − p), and /64 Subnets = 2^(64 − p).
Network prefix
N = IP AND Mask(p)128-bit AND.
Address count
2^(128 − p)IPv6 has no broadcast, so no reservation is subtracted.
/64 subnets
2^(64 − p)Valid for p ≤ 64.
Interface ID bits
128 − 64 = 64Standard SLAAC subnets use a 64-bit interface ID.
Worked example: 2001:db8:acad:1234::abcd/56
Network = 2001:db8:acad:1200::/56 Last = 2001:db8:acad:12ff:ffff:ffff:ffff:ffff Addresses = 2^72 = 4,722,366,482,869,645,213,696 /64 subnets = 2^8 = 256
IPv6 Subnet Calculator Conversion Table
The table lists 14 IPv6 prefix sizes with their address count, number of /64 subnets, and typical assignment.
| Prefix | Addresses | /64 Subnets | Typical Assignment |
|---|---|---|---|
| /32 | 7.92 × 10^28 | 4,294,967,296 | ISP / LIR allocation |
| /36 | 4.95 × 10^27 | 268,435,456 | Large regional block |
| /40 | 3.09 × 10^26 | 16,777,216 | Regional ISP block |
| /44 | 1.93 × 10^25 | 1,048,576 | Large enterprise |
| /48 | 1.20 × 10^24 | 65,536 | Enterprise site |
| /52 | 7.55 × 10^22 | 4,096 | Campus or large site |
| /56 | 4.72 × 10^21 | 256 | Home or small business |
| /60 | 2.95 × 10^20 | 16 | Small customer |
| /64 | 1.84 × 10^19 | 1 | Single LAN / VLAN |
| /112 | 65,536 | — | Some point-to-point links |
| /124 | 16 | — | Small server segment |
| /126 | 4 | — | Legacy point-to-point |
| /127 | 2 | — | Point-to-point link (RFC 6164) |
| /128 | 1 | — | Single interface / loopback |
What is IPv6 Subnet Calculator?
The IPv6 Subnet Calculator is a tool that returns the network prefix, address count, and /64 subnet count for any IPv6 address and prefix length.
IPv6 subnetting follows a different logic from IPv4. Address scarcity is not a concern, so the standard LAN subnet is always a /64, and planning focuses on how many /64 subnets a block contains. A /48 site prefix holds 65,536 of them.
IPv6 has no broadcast address. The calculator therefore subtracts no addresses for network and broadcast use, and it reports the full 2^(128 − p) count.
What are the uses of IPv6 Subnet Calculator?
There are 5 main uses of the IPv6 Subnet Calculator, including site planning, ISP delegation, and VLAN numbering.
Planning site prefixes
A /48 per site gives 65,536 /64 subnets, enough for every VLAN and future growth.
Sizing customer delegations
ISPs delegate a /56 (256 subnets) or a /60 (16 subnets) to customers through DHCPv6 Prefix Delegation.
Numbering VLANs
Each VLAN gets one /64. The calculator shows the prefix for each VLAN number.
Configuring router interfaces
Interface configuration needs the exact network prefix and length.
Explaining IPv6 scale
Address counts show why IPv6 planning centers on subnets rather than hosts.