What is a /16 subnet? 65,536 IPs and when a network needs that many addresses

How this is calculated

A /16 means the first 16 bits are the network portion, leaving 16 bits for hosts (2^16 = 65,536). In practice, you'd almost never put 65,000 devices on a single flat subnet. Broadcast traffic alone would cripple performance. Instead, /16 blocks are almost always sub-divided into smaller subnets (/20, /22, /24) for different departments, floors, or security zones. The /16 acts as a supernet or summary route that encompasses all the smaller subnets underneath it.

Verdict

The math is 16 bits reserved for the network and 16 bits for hosts, so 65,536 total addresses and 65,534 usable on a conventional IPv4 subnet. The reason you don't put 65,000 hosts on a flat L2 segment is broadcast traffic: ARP, DHCP, mDNS, and NetBIOS chatter would saturate the segment long before you filled the address space. Real deployments use the /16 as a supernet or summary route and carve it into operational subnets underneath, often /20 per availability zone and /22 per application tier. A /16 contains 16 separate /20 blocks, while the number of availability zones and provider-reserved addresses depends on the cloud platform and region. That's why AWS ships its default VPC at /16, not because anyone expects a flat 65K-host LAN.