/16 subnet mask (255.255.0.0)

A /16 network has 16 host bits, 65,536 addresses and 65,534 usable hosts. It is 256 /24 networks.

/16 at a glance

Netmask: 255.255.0.0
Wildcard mask: 0.0.255.255
Hex mask: 0xFFFF0000
Binary mask: 11111111.11111111.00000000.00000000
Host bits: 16
Total addresses: 65,536
Usable hosts: 65,534 (minus network and broadcast)
Compared with a /24: 256 /24 networks
Classful equivalent: Class B

Calculate a /16 in the subnet calculator

Typical uses of a /16

The /16 is the old Class B size and the largest CIDR block AWS allows for a VPC or a subnet. 192.168.0.0/16 (private) and 169.254.0.0/16 (link-local, where cloud metadata lives) are both /16s, as are Docker's default bridge 172.17.0.0/16 and Flannel's default pod network 10.244.0.0/16.

Well-known /16 blocks

192.168.0.0/16: Private network (RFC 1918); Calico default pod pool
169.254.0.0/16: Link-local / APIPA (RFC 3927); cloud metadata at 169.254.169.254
172.17.0.0/16: Docker default bridge network
10.244.0.0/16: Flannel default pod network

Example /16 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /16
10.0.0.0/16	10.0.0.0	10.0.0.1	10.0.255.254	10.0.255.255	10.1.0.0/16	calculate
172.16.0.0/16	172.16.0.0	172.16.0.1	172.16.255.254	172.16.255.255	172.17.0.0/16	calculate
192.168.0.0/16	192.168.0.0	192.168.0.1	192.168.255.254	192.168.255.255	192.169.0.0/16	calculate

How many /16s fit

In a	Number of /16 subnets
/8	256

What a /16 contains

Smaller block	How many
/24	256
/26	1,024
/28	4,096
/29	8,192
/30	16,384
/32	65,536

Splitting a /16

Into	Subnets	Usable hosts each
/17	2	32,766
/18	4	16,382
/19	8	8,190
/20	16	4,094

/16 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/16 allowed?	Usable after reservation
AWS VPC	/16 to /28	Yes	65,531 (5 reserved)
Azure VNet	/2 to /29	Yes	65,531 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	65,532 (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.