# /16 Subnet Mask (255.255.0.0) – Hosts, Range & FAQ > The /16 subnet mask is 255.255.0.0. A /16 block holds 65,536 addresses with 65,534 usable hosts — ranges, wildcard, binary math and FAQs. - Page URL: https://itinsighthub.com/subnet/16/ - Markdown variant of this page: append `?format=md` to any URL on this site or send `Accept: text/markdown`. - Full site index for AI assistants: https://itinsighthub.com/llms.txt - Full site export: https://itinsighthub.com/llms-full.txt # /16 Subnet Mask ReferenceIPv4 The classic campus block: x.x.0.0/16 packs 65,536 addresses, or 256 clean /24s, behind the memorably symmetric mask 255.255.0.0. From home routers to AWS VPCs, the /16 is where most network designs begin. The /16 subnet mask is 255.255.0.0, equivalent to 0.0.255.255 as a wildcard. A /16 block contains 65,536 IP addresses (65,534 usable hosts). ## /16 facts at a glance - **Subnet mask:** 255.255.0.0 - **Wildcard mask:** 0.0.255.255 - **Binary mask:** 11111111.11111111.00000000.00000000 - **Total addresses:** 65,536 - **Usable hosts:** 65,534 (excludes network & broadcast) - **Block size:** 65,536 addresses (216) - **Typical role:** Legacy Class B equivalent ## Example /16 networks Three consecutive /16 blocks, starting at the /16 boundary that contains 198.51.100.0: | Network | Usable range | Usable hosts | | --- | --- | --- | | 198.51.0.0/16 | 198.51.0.1 – 198.51.255.254 | 65,534 | | 198.52.0.0/16 | 198.52.0.1 – 198.52.255.254 | 65,534 | | 198.53.0.0/16 | 198.53.0.1 – 198.53.255.254 | 65,534 | ## How to calculate a /16 mask A /16 mask sets the first 16 bits of a 32-bit number to 1 and leaves the remaining 16 bits as 0. In binary that reads `11111111.11111111.00000000.00000000`, which converts to dotted decimal `255.255.0.0`. Each block covers a contiguous run of 216 = 65,536 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving `0.0.255.255`. ## Where /16 is used - Consumer networking: home routers live inside RFC 1918's 192.168.0.0/16, typically serving a /24 slice such as 192.168.1.0/24. - Cloud ceilings: AWS caps a VPC's primary CIDR at /16, and its default VPC is famously 172.31.0.0/16. - Campus cores that advertise one /16 summary at the border and keep interior routing tables short. - Route-summarization teaching, because 256 /24s collapsing into one line demonstrates the power of CIDR instantly. Usable hosts come to 65,534: the lowest address names the network and the highest is the broadcast. Clean subdivisions make planning easy: two /17s, four /18s, or 512 /25s all tile a /16 perfectly. ## Frequently asked questions **How many usable hosts are in a /16?** 65,534 of 65,536 total addresses. The two reserved slots are the network identifier and the broadcast address. **How many /24s are in a /16?** 256. The third octet counts straight from 0 to 255, giving you 256 individually routable LANs inside one summary. **What is 192.168.0.0/16?** The smallest RFC 1918 private range. Everything from 192.168.0.0 through 192.168.255.255 is reusable behind NAT and unroutable publicly, which is why nearly every home router uses it. **Is a /16 too big for one flat LAN?** As a single broadcast domain, yes: tens of thousands of ARP-speaking hosts create needless churn. Keep the /16 as your allocation and carve it into /22 to /24 segments per switch or VLAN. ## Open this block in a calculator [Open the /16 block in the subnet calculator](https://itinsighthub.com/subnet-calculator/?q=198.51.0.0%2F16) [Get the /16 wildcard mask →](https://itinsighthub.com/wildcard-mask-calculator/?q=%2F16) ### Related prefixes [/15](https://itinsighthub.com/subnet/15/)[/17](https://itinsighthub.com/subnet/17/)[/24](https://itinsighthub.com/subnet/24/)[/26](https://itinsighthub.com/subnet/26/)[/28](https://itinsighthub.com/subnet/28/)[/30](https://itinsighthub.com/subnet/30/) ← /15 subnet mask /17 subnet mask → --- © 2026 ITInsightHub · [About](https://itinsighthub.com/about/) · [Contact](https://itinsighthub.com/contact/) · [Privacy](https://itinsighthub.com/privacy/)