How Many Usable Hosts Are in a /27 Subnet?
A /27 IPv4 subnet contains 32 total addresses and 30 traditional usable host addresses. See the mask, block size, ranges, and worked examples.
32
total addresses
30
usable hosts
A /27 has 32 total addresses and 30 traditional usable hosts
A /27 IPv4 subnet contains 32 total addresses. In a traditional multi-access subnet, 30 are assignable to hosts because one address identifies the network and one is the directed broadcast address. The subnet mask is 255.255.255.224 and boundaries advance in blocks of 32 in the relevant octet.
| Property | /27 value | What it means |
|---|---|---|
| Prefix length | /27 | 27 network bits and 5 host bits |
| Subnet mask | 255.255.255.224 | The final mask octet is 11100000 in binary |
| Wildcard mask | 0.0.0.31 | The inverse of the subnet mask |
| Total addresses | 32 | 2 raised to the 5 remaining host bits |
| Traditional usable hosts | 30 | Total minus network and broadcast |
| Block increment | 32 | Network boundaries occur at 0, 32, 64, 96… |
Why the answer is 30 usable hosts
IPv4 addresses have 32 bits. The /27 prefix assigns 27 of those bits to the network portion, leaving 5 bits for addresses inside the block.
2^(32 − 27) = 2^5 = 32 total addresses
32 total − 1 network − 1 broadcast = 30 usable hosts
The “minus two” rule is appropriate for this ordinary /27 example, but it is not a universal formula for every prefix. RFC 3021 defines /31 point-to-point links where both addresses represent endpoints, and a /32 represents one host route. Those exceptions do not change the conventional 30-host result for /27.
Worked example: 192.168.1.64/27
This block begins at 64 and contains 32 addresses, so it ends at 64 + 31 = 95. The first and last values are the network and broadcast addresses. Removing those endpoints leaves .65 through .94, which is an inclusive range of 30 addresses.
Notice that the slash prefix describes the whole block, not one device. Writing192.168.1.77/27 on a host means that .77 belongs to the /27 block whose network address is192.168.1.64.
How to find the /27 network for any IPv4 address
When the first three octets are fully covered by the prefix, focus on the final octet. A /27 mask has an increment of 32, producing boundary values of 0, 32, 64, 96, 128, 160, 192, and 224.
- Take the final octet of the IP address.
- Find the largest multiple of 32 that does not exceed it.
- That multiple is the network value in the final octet.
- Add 31 to find the broadcast value.
- Add 1 to the network and subtract 1 from the broadcast for the traditional host range.
Binary AND produces the same result. The mask's final octet is 11100000. Applying it to the address keeps the first three bits of the final octet and clears the five host bits, yielding the network boundary.
You can also derive the increment directly from the mask: 256 − 224 = 32. This shortcut works in the octet where the mask changes from full network bits to host bits. It is useful for paper calculations, but a bitwise calculation is less error-prone when the prefix boundary falls in an earlier octet.
Common mistakes when reading a /27 range
Confusing total addresses with usable hosts
The power-of-two calculation gives 32 addresses in the block. It does not directly give the conventional host count. For an ordinary /27 LAN, remove the network and broadcast endpoints to reach 30.
Assuming only .0 and .255 can be special
Network and broadcast values depend on the prefix boundary. In a /27, .32, .64, .96, and the other multiples of 32 can be network addresses. Values .31, .63, .95, and the corresponding block endpoints can be broadcast addresses. The final octet alone is not enough without the mask.
Starting a /27 at an unaligned address
A valid /27 network begins on a multiple-of-32 boundary in the relevant octet. For example,192.168.1.70/27 is a host notation inside 192.168.1.64/27; it is not a new block beginning at .70.
Changing the arithmetic for private addresses
The /27 block size is the same for private and public IPv4 space. Whether the prefix begins with 10, 172.16–31, 192.168, or a public range does not change its 32 total addresses. Routing policy and address ownership change; the CIDR mathematics does not.
A /24 splits into eight equal /27 subnets
Moving from /24 to /27 borrows three additional bits for subnet identification. Three borrowed bits create2³ = 8 subnets. Each contains 32 total addresses and 30 conventional host addresses.
| Subnet | Network | Usable final octets | Broadcast |
|---|---|---|---|
| 192.168.1.0/27 | .0 | .1–.30 | .31 |
| 192.168.1.32/27 | .32 | .33–.62 | .63 |
| 192.168.1.64/27 | .64 | .65–.94 | .95 |
| 192.168.1.96/27 | .96 | .97–.126 | .127 |
| 192.168.1.128/27 | .128 | .129–.158 | .159 |
| 192.168.1.160/27 | .160 | .161–.190 | .191 |
| 192.168.1.192/27 | .192 | .193–.222 | .223 |
| 192.168.1.224/27 | .224 | .225–.254 | .255 |
This table uses all eight definable /27 blocks, including the first and last subnets. Excluding the all-zero and all-one subnets is an obsolete classful practice; modern CIDR planning uses the complete set of aligned blocks.
For a broader comparison of adjacent prefixes, masks, and host counts, use the IPv4 subnet mask and CIDR cheat sheet.
Is a /27 large enough for 30 devices?
Mathematically, a traditional /27 offers 30 assignable host addresses. Operationally, filling every address leaves no room for growth and may overlook infrastructure such as a router interface, firewall, access points, printers, monitoring appliances, or virtual IPs.
| Prefix | Mask | Total | Traditional usable |
|---|---|---|---|
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
If the requirement is exactly 30 endpoints, a /27 is usually too tight once network infrastructure and growth are considered. A /26 offers 62 conventional host addresses. If isolation matters more than spare capacity, several smaller subnets may be preferable—but that is a network-design decision, not simply a host count calculation.
Common questions about /27 networks
Does /27 mean there are 27 IP addresses?
No. The 27 is the number of network-prefix bits. Five of the 32 IPv4 bits remain, so the block contains2⁵ = 32 addresses.
What is the wildcard mask for /27?
It is 0.0.0.31. The wildcard mask is the bitwise inverse of255.255.255.224 and marks the five variable host bits in the final octet.
How many /27 subnets fit inside a /24?
Eight. The three additional prefix bits create 2³ aligned blocks, beginning at final-octet values 0, 32, 64, 96, 128, 160, 192, and 224.
Is 255.255.255.224 always /27?
Yes for an IPv4 subnet mask. Its binary form contains 27 consecutive one bits followed by five zero bits, which is exactly the /27 prefix definition.