Infrastructure / BROWSER-ONLY UTILITY
IPv4 CIDR Calculator
Work out the address arithmetic without turning it into a claim about available or reachable hosts. This calculator does not scan a subnet.
Enter an address such as 192.0.2.129 and choose a prefix from 0 to 32. IPv6 addresses and dotted netmask notation are not supported. Limit: 100,000 characters.
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Result
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What is calculated
The result includes normalised CIDR, network address, first and last addresses, subnet mask, wildcard mask and total address count. Input does not need to be the network endpoint: 192.0.2.129/24 belongs to 192.0.2.0/24. Leading-zero octets, abbreviated or hexadecimal addresses and dotted netmask suffixes are rejected so the tool does not silently reinterpret them.
Ordinary host arithmetic
For prefixes shorter than /31, the displayed host count subtracts the network and directed-broadcast endpoints. The first and last assumed host values follow that arithmetic. This is not a pool-allocation decision. Special-purpose ranges, organisation policy, gateway reservations, cloud networking rules and other constraints can make additional addresses unsuitable for assignment.
The /31 and /32 cases
A /31 is interpreted using the RFC 3021 point-to-point convention: two endpoint addresses and no directed broadcast. Confirm that both devices and the intended topology support that convention. A /32 represents a single host route, with one address and no distinct network or directed-broadcast endpoint. These cases are not reduced to zero hosts by the ordinary subtraction rule.
The /0 boundary
A /0 covers all 4294967296 IPv4 addresses. Its mask is 0.0.0.0 and its range ends at 255.255.255.255. Any displayed usable count remains a mathematical convention, not a list of allocatable addresses. The tool performs no discovery, ping, port scan, route lookup or reachability check, regardless of the size of the supplied prefix.
References
Documentation reviewed: . Rule results describe the supplied text, not a live application test.
Useful next steps
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