IPv6 subnet calculator
Find the exact start, end and size of one IPv6 prefix.
- 1Add input
- 2Review and run
- 3Get your result
Tool input and files are processed in this browser without being uploaded.
Before you start
Enter one IPv6 address and /0–/128 prefix. See the normalized network, inclusive range and exact address count, then copy a field or download JSON. The mathematical range does not prove those addresses were assigned to you.
How to use this tool
- Paste one IPv6 address and prefix, such as 2001:db8::1/64. Spaces around the slash are accepted.
- Check the normalized network preview and exact address count before calculating.
- Read the inclusive start and end, copy the field you need, or download the complete JSON. Confirm the provider allocation before configuring addresses.
Supported inputs and limits
One IPv6 address and prefix per run. A zone ID, port, address list or file is not accepted.
This is exact local arithmetic, not a provider allocation, routing, DNS or reachability check. IPv6 has no broadcast address.
The count remains a decimal string in JSON so values beyond JavaScript safe integers are not rounded.
Worked example
Example input
2001:db8::1/64
Example options
{}Example output
{
"inputAddress": "2001:db8::1",
"networkCidr": "2001:db8::/64",
"network": "2001:db8::",
"lastAddress": "2001:db8::ffff:ffff:ffff:ffff",
"prefix": 64,
"hostBits": 64,
"addresses": "18446744073709551616"
}When something does not work
Enter one valid IPv6 address followed by a decimal /0–/128 prefix. Remove a %zone, brackets, port or extra lines; check your provider allocation separately.
Frequently asked questions
Does this range show all addresses assigned to my server?
No. It shows the mathematical boundaries of the prefix. A hosting provider may route or assign only specific addresses even when several servers share the same /64.
Where is the IPv6 broadcast or usable-host count?
IPv6 has no broadcast address. The range end is only a numeric boundary. The number of addresses is exact but does not promise that each value can be configured.
What happens if the input has host bits set or uses /0 or /128?
The network start is normalized to the prefix boundary. /0 spans the full 128-bit address space; /128 is one address. Both are calculated exactly.
Is my input sent to a server?
No. Calculation runs in your browser. Save any results you need before closing the tab.
Documentation & further reading
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