The /27 prefix: 32 addresses, the small-VLAN standard
A /27 has 5 host bits: 32 addresses, mask 255.255.255.224. The last octet breaks into eighths — .0, .32, .64 and so on — giving eight /27s per /24.
Ask a network engineer to size a printer VLAN, a camera network, or a small lab segment and the reflex answer is /27. Thirty usable hosts, tidy boundaries, and no meaningful waste.
| Prefix length | /27 |
| Subnet mask | 255.255.255.224 |
| Wildcard mask | 0.0.0.31 |
| Total addresses | 32 |
| Usable hosts | 30 |
Sizing VLANs the /27 way
The discipline of /27 is deliberate restraint: if a segment will never hold more than about twenty devices, a /27 gives it room plus headroom and no more. Tight subnets force honest accounting — when the team that swore they needed five devices asks for address number twenty-five, you finally get the conversation about what is actually plugged in.
The overhead starts to bite
At /27 the fixed cost of subnetting becomes visible: you lose 2 of 32 addresses, about 6%, to the network and broadcast entries. Split a /24 into eight /27s and you keep 240 of the original 254 usable addresses. That tax doubles with every further split, which is the argument against subdividing just in case.
CIDR Calculator
Run the math on 10.0.0.0/27 — or any other block
Frequently asked questions
How many IP addresses are in a /27?
32 in total (2^5), of which 30 are usable for hosts.
What is the subnet mask of a /27?
255.255.255.224. Three network bits in the last octet mean /27 networks start on multiples of 32.
How many /27s are in a /24?
Eight, beginning at .0, .32, .64, .96, .128, .160, .192, and .224.
What would you use a /27 for?
Small fixed-purpose VLANs: printers, cameras, building automation, a lab bench, or a point-of-sale segment — roughly thirty devices or fewer with stable membership.