/27 subnet mask (255.255.255.224)

A /27 network has 5 host bits, 32 addresses and 30 usable hosts. It is 1/8 of a /24.

/27 at a glance

Netmask: 255.255.255.224
Wildcard mask: 0.0.0.31
Hex mask: 0xFFFFFFE0
Binary mask: 11111111.11111111.11111111.11100000
Host bits: 5
Total addresses: 32
Usable hosts: 30 (minus network and broadcast)
Compared with a /24: 1/8 of a /24

Calculate a /27 in the subnet calculator

Typical uses of a /27

A /27 has 30 usable hosts. Microsoft recommends a /27 or larger for an Azure GatewaySubnet (VPN and ExpressRoute gateways). It suits small server VLANs and management networks.

Example /27 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /27
10.0.0.0/27	10.0.0.0	10.0.0.1	10.0.0.30	10.0.0.31	10.0.0.32/27	calculate
172.16.0.0/27	172.16.0.0	172.16.0.1	172.16.0.30	172.16.0.31	172.16.0.32/27	calculate
192.168.1.0/27	192.168.1.0	192.168.1.1	192.168.1.30	192.168.1.31	192.168.1.32/27	calculate
203.0.113.0/27	203.0.113.0	203.0.113.1	203.0.113.30	203.0.113.31	203.0.113.32/27	calculate

The /27 boundary falls in the fourth octet, so /27 networks start every 32 in that octet (8 per /24): 0, 32, 64, 96, 128, 160, 192, 224.

How many /27s fit

In a	Number of /27 subnets
/8	524,288
/16	2,048
/20	128
/24	8

What a /27 contains

Smaller block	How many
/28	2
/29	4
/30	8
/32	32

Splitting a /27

Into	Subnets	Usable hosts each
/28	2	14
/29	4	6
/30	8	2
/31	16	2

/27 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/27 allowed?	Usable after reservation
AWS VPC	/16 to /28	Yes	27 (5 reserved)
Azure VNet	/2 to /29	Yes	27 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	28 (4 reserved)

Cloud providers reserve addresses in every subnet (first four and the last address (network, VPC router, DNS, future use, broadcast) on AWS), so the usable count there differs from the classic 2^n - 2.