Online Tool Store
Subnet Mask Cheat Sheet
Subnet Mask Cheat Sheet is the lookup table; the minus two is the part people forget when sizing a subnet. Runs entirely in your browser with no upload and no.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Networking
Subnet Mask Cheat Sheet
Frontend preview — no upload or external service.
Subnet Reference
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How the Subnet Mask Cheat Sheet works
- Find the prefix length you are working with, or the host count you need.
- Read across for the mask, the wildcard mask and the usable host count.
- Remember that usable hosts is two fewer than total addresses on a normal subnet, because of the network and broadcast addresses.
The method
A prefix length says how many leading bits are the network portion; the rest address hosts.
usable hosts = 2^(32 - prefix) - 2
The two subtracted are the all-zeros network address and the all-ones broadcast address, neither of which can be assigned to a host.
FAQ
Why are two addresses unusable?
The all-zeros address identifies the network itself and the all-ones address is the broadcast address. Neither can be assigned, which is why a /24 gives 254 hosts rather than 256.
What is a wildcard mask?
The bitwise inverse of a subnet mask, used in access control lists on some network equipment. A /24 mask of 255.255.255.0 has a wildcard of 0.0.0.255.
Does the minus two rule apply to IPv6?
No. IPv6 has no broadcast address and subnets are conventionally /64 regardless of host count, so the arithmetic that governs IPv4 subnetting largely does not carry over.
How we compare
| Feature | Online Tool Store | A terminal utility | A hosted diagnostics service |
|---|---|---|---|
| Full prefix table | ✓ | Calculator only | ✓ |
| Wildcard masks | ✓ | ✗ | ✓ |
| Works offline once loaded | ✓ | ✗ | Printed |
| No sign-up | ✓ | ✓ | ✗ |
Subnet Mask Cheat Sheet is the lookup table; the minus two is the part people forget when sizing a subnet.