/27 Subnet Mask ReferenceIPv4
Thirty addresses per bite: mask <code>255.255.255.224</code> tucks eight /27s into every /24. This is where VLAN carving turns surgical, as one legacy block becomes eight purpose-built micro-segments.
/27 facts at a glance
- Subnet mask
- 255.255.255.224
- Wildcard mask
- 0.0.0.31
- Binary mask
- 11111111.11111111.11111111.11100000
- Total addresses
- 32
- Usable hosts
- 30 (excludes network & broadcast)
- Block size
- 32 addresses (25)
- Typical role
- Subnets, VLANs and WAN links
Example /27 networks
Three consecutive /27 blocks, starting at the /27 boundary that contains 198.51.100.0:
| Network | Usable range | Usable hosts |
|---|---|---|
| 198.51.100.0/27 | 198.51.100.1 – 198.51.100.30 | 30 |
| 198.51.100.32/27 | 198.51.100.33 – 198.51.100.62 | 30 |
| 198.51.100.64/27 | 198.51.100.65 – 198.51.100.94 | 30 |
How to calculate a /27 mask
A /27 mask sets the first 27 bits of a 32-bit number to 1 and leaves the remaining 5 bits as 0. In binary that reads 11111111.11111111.11111111.11100000, which converts to dotted decimal 255.255.255.224. Each block covers a contiguous run of 25 = 32 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 0.0.0.31.
Where /27 is used
- Per-department micro-VLANs sliced from an existing /24.
- Isolated storage or iSCSI segments that must never see user traffic.
- Education labs where each bench gets its own small subnet.
Boundaries sit at .0, .32, .64, .96, .128, .160, .192, and .224, each block carrying 30 usable hosts.
Historical footnote: before RFC 3021 legitimized /31 links, engineers routinely burned a /30 (or worse) on every router-to-router circuit; modern designs reclaim that space.
Frequently asked questions
How many usable hosts are in a /27?
30 of 32 total addresses.
What is the subnet mask for a /27?
<code>255.255.255.224</code>, wildcard <code>0.0.0.31</code>: three borrowed bits yield eight subnets per /24.
How many /27s are in a /24?
Eight.
What is the broadcast address of the 192.168.1.32/27 block?
<code>192.168.1.63</code>; the block spans .32 through .63 with hosts at .33 through .62.
Open this block in a calculator
Open the /27 block in the subnet calculator