Usable Hosts Calculator
Finds the right subnet size for the number of devices you have.
Smallest subnet
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Subnet mask —
Usable hosts —
Spare addresses —
Nearby sizes
Reading this —
The formula
usable hosts = 2^(32 − prefix) − 2
The exceptions are a /31, with 2 usable addresses, and a /32, with 1.
What to watch out for
Remember to count the router, servers and any address pool you reserve.
Frequently Asked Questions
What subnet holds 50 hosts?
A /26, with 62 usable addresses.
What subnet holds 500 hosts?
A /23, with 510 usable addresses.