/18 subnet mask (255.255.192.0)

A /18 network has 14 host bits, 16,384 addresses and 16,382 usable hosts. It is 64 /24 networks.

/18 at a glance

Netmask: 255.255.192.0
Wildcard mask: 0.0.63.255
Hex mask: 0xFFFFC000
Binary mask: 11111111.11111111.11000000.00000000
Host bits: 14
Total addresses: 16,384
Usable hosts: 16,382 (minus network and broadcast)
Compared with a /24: 64 /24 networks

Calculate a /18 in the subnet calculator

Typical uses of a /18

A /18 (16,384 addresses) is a popular size for EKS or GKE pod ranges when each node takes a block of pod IPs, and for splitting a /16 VPC into four zones.

Example /18 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /18
10.0.0.0/18	10.0.0.0	10.0.0.1	10.0.63.254	10.0.63.255	10.0.64.0/18	calculate
172.16.0.0/18	172.16.0.0	172.16.0.1	172.16.63.254	172.16.63.255	172.16.64.0/18	calculate
192.168.0.0/18	192.168.0.0	192.168.0.1	192.168.63.254	192.168.63.255	192.168.64.0/18	calculate

The /18 boundary falls in the third octet, so /18 networks start every 64 in that octet (4 per /16): 0, 64, 128, 192.

How many /18s fit

In a	Number of /18 subnets
/8	1,024
/16	4

What a /18 contains

Smaller block	How many
/24	64
/26	256
/28	1,024
/29	2,048
/30	4,096
/32	16,384

Splitting a /18

Into	Subnets	Usable hosts each
/19	2	8,190
/20	4	4,094
/21	8	2,046
/22	16	1,022

/18 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/18 allowed?	Usable after reservation
AWS VPC	/16 to /28	Yes	16,379 (5 reserved)
Azure VNet	/2 to /29	Yes	16,379 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	16,380 (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.