# /27 Subnet Mask (255.255.255.224) – Hosts, Range & FAQ

> The /27 subnet mask is 255.255.255.224. A /27 block holds 32 addresses with 30 usable hosts — ranges, wildcard, binary math and FAQs.

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# /27 Subnet Mask ReferenceIPv4

Thirty addresses per bite: mask 255.255.255.224 tucks eight /27s into every /24. This is where VLAN carving turns surgical, as one legacy block becomes eight purpose-built micro-segments.

The /27 subnet mask is 255.255.255.224, equivalent to 0.0.0.31 as a wildcard. A /27 block contains 32 IP addresses (30 usable hosts).

## /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?**

255.255.255.224, wildcard 0.0.0.31: 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?**

192.168.1.63; 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](https://itinsighthub.com/subnet-calculator/?q=198.51.100.0%2F27)

[Get the /27 wildcard mask →](https://itinsighthub.com/wildcard-mask-calculator/?q=%2F27)

### Related prefixes

[/24](https://itinsighthub.com/subnet/24/)[/26](https://itinsighthub.com/subnet/26/)[/28](https://itinsighthub.com/subnet/28/)[/30](https://itinsighthub.com/subnet/30/)

← /26 subnet mask
/28 subnet mask →

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