Subnet Calculator

Calculate IPv4 and IPv6 subnets, dotted and wildcard masks, usable-host semantics, exact address counts, equal splits and VLSM plans. See the bit boundary, size networks from requirements, and export implementation-ready tables.

Local network math · no signup

Address & prefix

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CIDR, IPv4 mask, or wildcard

Dotted value interpretation

Host addresses are accepted and normalized to their containing network.

Network / host bit boundary

Subnet details

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Total addresses—

Usable hosts*—

Host bits—

Legacy class—

* IPv4 uses traditional subnet host semantics, with RFC 3021 handling for /31 point-to-point links and a single address for /32. IPv6 has no broadcast address, so “usable” is shown as the full mathematical block.

Size by required hosts

Required usable IPv4 hosts

Allow /31 for exactly two point-to-point endpoints

Ready.

Size by subnet count

Parent prefix

Needed subnets

Ready.

Variable-length plan

Parent IPv4 block

Requirements · name, hosts

Largest requirements are allocated first to minimize fragmentation.

Allocation table

Name	Hosts needed	CIDR	Usable range	Capacity
Build a plan to see allocations.

Equal-size splitter

Parent block

New prefix

Ready.

Child networks

IPv4 host rules

For ordinary IPv4 subnets, the all-zero host value identifies the network and the all-one host value is broadcast, so two addresses are traditionally unavailable to hosts. /31 is special for point-to-point links; /32 identifies one address.

IPv6

IPv6 does not use broadcast addresses. The calculator therefore reports the entire mathematical range and exact 128-bit address count. Output uses canonical compressed text formatting.