Subnet Mask to CIDR
Convert between prefix length and subnet mask, with host counts.
System verdict
RESULT/24 = 255.255.255.0 — 254 usable hosts
Usable hosts are two fewer than the total, because the first address is the network and the last is the broadcast.
- Prefix length
- /24
- Subnet mask
- 255.255.255.0
- Wildcard mask
- 0.0.0.255
- Total addresses
- 256
- Usable hosts
- 254
What this cannot tell you
- Pure arithmetic on the definition of a subnet mask. There is nothing here that can drift or need updating.
- IPv4 only.
How this calculation works
A subnet mask is simply a run of ones followed by a run of zeros: the prefix length says how many ones. This tool converts either form to the other and counts the hosts, using the definition directly rather than a lookup table, so any prefix from /0 to /32 works.
What the results mean
- Wildcard mask
- The inverse of the subnet mask, used by Cisco access lists and some routing configurations.
- Usable hosts
- Two fewer than the total for /30 and larger, because the network and broadcast addresses are reserved. A /31 and /32 are the exceptions.
Frequently asked questions
Why does a /24 give 254 hosts, not 256?
The first address identifies the network and the last is the broadcast, and neither can be assigned to a device. So 256 total addresses leave 254 usable.
Is 255.255.255.0 the same as /24?
Yes. That mask is 24 ones followed by 8 zeros, which is exactly what /24 means. Enter either form above to see the other.