IPv6 Subnet Calculator
Enter the allocated prefix and the subnet size to get counts.
Your numbers
Your results
Number of subnets
Number of subnets
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Subnets (plain number if small)
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Addresses per subnet
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Addresses in the allocation
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Number of /64 networks in the allocation
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IPv6 Subnet Calculator by TheCalcTools
How the IPv6 Subnet Calculator works
Enter the prefix your provider or RIR gave you and the prefix you want per subnet.
The subnet count is 2^(m − n) and each subnet holds 2^(128 − m) addresses.
Use /64 on LAN segments; SLAAC requires it.
The formula
Subnets = 2^(m − n)Addresses = 2^(128 − m)
Worked example
Using the default values shown in the calculator:
| Allocated prefix (/n) | 48 |
|---|---|
| Subnet prefix (/m) | 64 |
- A /48 split into /64s gives 2^16 = 65536 subnets.
- Each /64 holds 1.845 × 10^19 addresses.
Result:
| Number of subnets | 6.554 × 10^4 |
|---|---|
| Subnets (plain number if small) | 65536 |
| Addresses per subnet | 1.845 × 10^19 |
| Addresses in the allocation | 1.209 × 10^24 |
| Number of /64 networks in the allocation | 65536 |
Frequently asked questions
Why use /64 for every LAN?
SLAAC and many IPv6 features assume a 64-bit interface identifier, so /64 is the standard subnet size.
How many /64s are in a /48?
65,536.
Sources and further reading
- RFC 4291: IP Version 6 Addressing Architecture
- RFC 6177: IPv6 Address Assignment to End Sites
- Wikipedia: IPv6 address
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.