IPv4 subnet calculator
Calculate the network, broadcast, usable address range and host count from an IPv4 address with a CIDR prefix or subnet mask.
IPv6 subnet calculator
Expand or compress an IPv6 address and calculate its CIDR network, final address and exact address count for prefixes 0–128.
About this tool
Check a subnet boundary or normalize a long IPv6 address before adding it to a configuration.
How to use
Enter an IPv6 address with /prefix, or use the separate prefix field. Copy the compressed or fully expanded address, network CIDR, final address and exact number of addresses. Embedded IPv4 forms such as ::ffff:192.0.2.1 are accepted.
Compression follows RFC 5952: lowercase, the longest zero run, and the first run in a tie. Prefixes range from 0 to 128. IPv6 has no broadcast address; the result is not a claim that every address is assignable. Zone identifiers such as %eth0 are unsupported.
Common questions
Why is there no broadcast address?
IPv6 does not use broadcast addresses. The final address is the upper boundary of the calculated range, and the count does not mean every address can be assigned.
Why does the CIDR result remove part of my IPv6 address?
The CIDR result is the subnet’s network address, so host bits are set to zero. For example, 2001:db8::1234/64 becomes 2001:db8::/64. The compressed and expanded fields still show your input address. A prefix written in the address takes precedence over the separate prefix field.
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