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CIDR Calculator — Free Online Calculator

CIDR Calculator solves Usable hosts = 2^(32−prefix) − 2 — prefix = the CIDR suffix (e.g. /24), the −2 excludes the network and broadcast addresses (not subtracted for /31 and /32). Enter your known values and the calculator solves for the rest instantly. Everything is computed locally in your browser — your data never leaves your device. Completely free, with no account required.

How to use CIDR Calculator

1. Enter your known values in the fields.
2. The result updates instantly as you type.
3. Copy or note down the result.

Frequently asked questions

What formula does CIDR Calculator use?

Usable hosts = 2^(32−prefix) − 2 — prefix = the CIDR suffix (e.g. /24), the −2 excludes the network and broadcast addresses (not subtracted for /31 and /32).

Can I use it on my phone?

Yes. The layout adapts to small screens and behaves the same on mobile as on desktop.

Is my input saved anywhere?

No. Values stay in your browser and are gone as soon as you close the tab.

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