# /28 Subnet Mask (255.255.255.240) – Hosts, Range & FAQ > The /28 subnet mask is 255.255.255.240. A /28 block holds 16 addresses with 14 usable hosts — ranges, wildcard, binary math and FAQs. - Page URL: https://itinsighthub.com/subnet/28/ - 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 # /28 Subnet Mask ReferenceIPv4 Sixteen addresses, fourteen hosts, mask 255.255.255.240, unless you are in the cloud, where the honest answer is eleven. The /28 is the default currency of AWS and Azure subnet sizing. The /28 subnet mask is 255.255.255.240, equivalent to 0.0.0.15 as a wildcard. A /28 block contains 16 IP addresses (14 usable hosts). ## /28 facts at a glance - **Subnet mask:** 255.255.255.240 - **Wildcard mask:** 0.0.0.15 - **Binary mask:** 11111111.11111111.11111111.11110000 - **Total addresses:** 16 - **Usable hosts:** 14 (excludes network & broadcast) - **Block size:** 16 addresses (24) - **Typical role:** Subnets, VLANs and WAN links ## Example /28 networks Three consecutive /28 blocks, starting at the /28 boundary that contains 198.51.100.0: | Network | Usable range | Usable hosts | | --- | --- | --- | | 198.51.100.0/28 | 198.51.100.1 – 198.51.100.14 | 14 | | 198.51.100.16/28 | 198.51.100.17 – 198.51.100.30 | 14 | | 198.51.100.32/28 | 198.51.100.33 – 198.51.100.46 | 14 | ## How to calculate a /28 mask A /28 mask sets the first 28 bits of a 32-bit number to 1 and leaves the remaining 4 bits as 0. In binary that reads `11111111.11111111.11111111.11110000`, which converts to dotted decimal `255.255.255.240`. Each block covers a contiguous run of 24 = 16 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving `0.0.0.15`. ## Where /28 is used - Cloud VPC subnets for small application tiers and databases. - DMZ segments holding load balancers and jump boxes. - Tight public assignments carved from a provider's block. AWS and Azure each reserve five addresses in every subnet (network, gateway/DNS plumbing, and broadcast), so a /28 subnet yields 11 usable instances rather than the textbook 14. AWS permits subnets between /16 and /28, which makes the /28 the smallest subnet you can possibly create there. ## Frequently asked questions **How many hosts are in a /28?** 14 by the classic count of 16 addresses minus network and broadcast. On AWS or Azure, expect 11 usable because each platform reserves five addresses per subnet. **What does 255.255.255.240 mean?** It is the /28 mask: twenty-eight fixed bits leave exactly four host bits, so blocks come in sixteen-address units aligned on multiples of sixteen. **How many /28s are in a /24?** Sixteen, one for each multiple-of-sixteen boundary in the fourth octet (.0, .16, .32, and so on). **Why does my cloud console show fewer free IPs than my calculator?** Cloud providers withhold five addresses per subnet for internal services; calculators apply only the textbook minus-two rule. ## Open this block in a calculator [Open the /28 block in the subnet calculator](https://itinsighthub.com/subnet-calculator/?q=198.51.100.0%2F28) [Get the /28 wildcard mask →](https://itinsighthub.com/wildcard-mask-calculator/?q=%2F28) ### Related prefixes [/24](https://itinsighthub.com/subnet/24/)[/26](https://itinsighthub.com/subnet/26/)[/27](https://itinsighthub.com/subnet/27/)[/29](https://itinsighthub.com/subnet/29/)[/30](https://itinsighthub.com/subnet/30/) ← /27 subnet mask /29 subnet mask → --- © 2026 ITInsightHub · [About](https://itinsighthub.com/about/) · [Contact](https://itinsighthub.com/contact/) · [Privacy](https://itinsighthub.com/privacy/)