Subnet Calculator help

Quick start

1. Enter an IPv4 or IPv6 address, with or without a CIDR prefix.
2. If the address has no prefix, choose one from the Prefix control or accept the default.
3. Select Calculate or press Enter.
4. Review the normalized network, range, masks, totals, address type, and reverse-DNS form.
5. Use the Divide table to split the network into halves or join siblings back together.

Calculation details

• The result is the network containing the entered address. For example, 192.168.1.130/25 belongs to 192.168.1.128/25.
• IPv4 results include broadcast, usable-host range, netmask, wildcard mask, binary values, class, and PTR form.
• IPv6 results include the address range, expanded address and network, address type, totals, and nibble-aligned reverse-DNS form where applicable.
• Split replaces one row with its two equal children. Join collapses the selected leaf and its sibling back to their parent.

Subnetting tips

• Recalculating a different address or prefix starts a new divide tree.
• IPv4 /31 and /32 networks have special host semantics; use the displayed totals and ranges in the context of your protocol.
• IPv6 networks contain very large address counts, so the tool formats totals without converting them to unsafe JavaScript numbers.
• Copy share link preserves the calculated network and current split tree in the URL.

Privacy and saved data

All arithmetic runs locally and the tool stores nothing in localStorage. Deep links expose the address and prefix in the path. A share link deliberately encodes the current network and split state in its config query parameter, so anyone receiving the URL can recover that state.

Troubleshooting

• IPv4 prefixes must be 0–32 and IPv6 prefixes 0–128.
• If the prefix selector appears to disagree with the input, the explicit /prefix in the input takes precedence when you calculate.
• A subnet can only be joined with its sibling from the same split; unrelated adjacent blocks are not merged.