/28 Subnet Mask ReferenceIPv4
Sixteen addresses, fourteen hosts, mask <code>255.255.255.240</code>, unless you are in the cloud, where the honest answer is eleven. The /28 is the default currency of AWS and Azure subnet sizing.
/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