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CIDR Calculator

Compute the network, broadcast, usable host range and address counts for any IPv4 CIDR block or address/prefix pair.

Input

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Output

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Questions
Does this support IPv6?
No. This version is IPv4 only — entering an IPv6 address or a prefix greater than 32 is treated as an invalid address/prefix and rejected with an error. IPv6 CIDR math (128-bit, no broadcast concept) is different enough that it would need its own tool.
I entered a host address like 192.168.1.5/24, not the network address 192.168.1.0/24 — is that a mistake?
No, that is normal CIDR usage. The tool always derives the network address by masking whatever address you give it, so 192.168.1.5/24 and 192.168.1.0/24 report the same network, broadcast and usable range — only the “IP address” line in the results reflects what you actually typed.
Why does a /31 show 2 usable hosts instead of 0?
Per RFC 3021, /31 is a special case for point-to-point links: both addresses in the two-address block are usable and there is no separate network or broadcast address. The tool implements this explicitly rather than applying the normal “subtract 2” rule, which would incorrectly yield 0 usable hosts for a real-world case that needs 2.
What does a /32 mean here?
A /32 is a single host route — the block contains exactly one address, which is simultaneously the network, broadcast, first-usable and last-usable address, and the usable host count is 1.
        
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