Subnet / CIDR calculator
Work out network, broadcast, host counts, and ranges for IPv4 and IPv6.
The subnet calculator does the CIDR math for you — entirely in your browser, no network calls. It handles both IPv4 and IPv6.
What it computes
- Network and broadcast addresses (IPv4).
- First and last usable host, and total host count.
- The full address range for an IPv6 prefix.
203.0.113.0/24 -> 256 addresses, hosts .1–.254
2a0e:xxxx::/44 -> first 2a0e:xxxx::, 2^84 addressesOpen it under Tools → Subnet.