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CIDR / Subnet Host Calculator
Subnet mask and usable host count for a CIDR prefix.
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How it works
Total addresses = 2^(32 − prefix). Usable hosts normally subtract the network and broadcast addresses, so a /24 has 256 addresses and 254 usable hosts. /31 links use both addresses and /32 is a single host. Example: with the default values, subnet mask comes to 255.255.255.0.
FAQ
Is this calculator free?
Yes. No signup is needed and nothing you enter is stored.
Is the result exact?
Results are rounded for display. For financial, medical, or legal decisions, confirm with a professional.
Do my numbers leave my device?
No. The calculation runs in your browser.