Last reviewed: May 2026
A /27 subnet contains 32 total IP addresses and 30 usable host addresses. The "/27" prefix means 27 bits are used for the network portion, leaving 5 bits (25 = 32) for host addressing. The /27 is significant in Azure networking as the minimum required size for GatewaySubnet and RouteServerSubnet.
Calculate any /27 subnet instantly →| Property | Value |
|---|---|
| Prefix length | /27 |
| Subnet mask | 255.255.255.224 |
| Wildcard mask | 0.0.0.31 |
| Total addresses | 32 |
| Usable host addresses | 30 |
| Network address | x.x.x.0 (must align to multiples of 32: .0, .32, .64, …) |
| Broadcast address | x.x.x.31 (last address in the block) |
| Binary mask | 11111111.11111111.11111111.11100000 |
| AWS usable hosts | 27 (AWS reserves 5 IPs per subnet) |
| Azure usable hosts | 27 (Azure reserves 5 IPs per subnet) |
/27 is the minimum size required for Azure GatewaySubnet and RouteServerSubnet. Using a /28 for GatewaySubnet will cause deployment failures when provisioning VPN Gateway or ExpressRoute Gateway. Microsoft recommends /27 as the minimum and /26 or larger for production deployments with ExpressRoute coexistence. Always size your GatewaySubnet at /27 or larger.
| CIDR | Subnet Mask | Total IPs | Usable Hosts | Azure Usable | Typical Use |
|---|---|---|---|---|---|
| /26 | 255.255.255.192 | 64 | 62 | 59 | Azure Firewall, Bastion, App Gateway |
| /27 | 255.255.255.224 | 32 | 30 | 27 | Azure GatewaySubnet minimum; infrastructure |
| /28 | 255.255.255.240 | 16 | 14 | 11 | AWS minimum; too small for Azure GatewaySubnet |
A /24 block contains 2(27−24) = 8 subnets of /27 size. For example, 10.0.0.0/24 can be subdivided into 10.0.0.0/27, 10.0.0.32/27, 10.0.0.64/27, 10.0.0.96/27, 10.0.0.128/27, 10.0.0.160/27, 10.0.0.192/27, and 10.0.0.224/27. Each block starts on a multiple of 32.
Try the subnet splitter in SubnetSolver →A /27 subnet has 30 usable host addresses out of 32 total IPs. Two addresses are reserved: the network address and the broadcast address. In AWS, 27 IPs are usable (5 reserved by AWS). In Azure, 27 IPs are usable (5 reserved by Azure).
The subnet mask for a /27 network is 255.255.255.224. In binary, 27 bits are set to 1 followed by 5 bits of 0: 11111111.11111111.11111111.11100000.
A /24 network can be divided into 8 subnets of /27 size. The difference in prefix length is 27 - 24 = 3 bits, and 2^3 = 8. For example, 10.0.0.0/24 contains 10.0.0.0/27, 10.0.0.32/27, 10.0.0.64/27 through 10.0.0.224/27.