/28 · 255.255.255.240
Open in the calculator
16 addresses, 14 usable (11 in AWS after its five reserved addresses). The smallest subnet AWS allows. Used for tiny subnets such as bastion hosts, VPN endpoints or transit-gateway attachments.
Key numbers
| Prefix length | /28 (28 network bits, 4 host bits) |
| Subnet mask | 255.255.255.240 |
| Mask in binary | 11111111.11111111.11111111.11110000 |
| Wildcard mask | 0.0.0.15 |
| Total addresses | 16 |
| Usable hosts | 14 (total minus network and broadcast) |
| Fits in a /24 | 16 times |
| Block size | Increments of 16 in octet 4 |
Example ranges
Private (RFC 1918) blocks of this size. Click one to open it in the calculator.
| Block | First address | Last address | Usable hosts |
|---|---|---|---|
| 10.0.0.0/28 | 10.0.0.0 | 10.0.0.15 | 10.0.0.1 – 10.0.0.14 |
| 172.16.0.0/28 | 172.16.0.0 | 172.16.0.15 | 172.16.0.1 – 172.16.0.14 |
| 192.168.0.0/28 | 192.168.0.0 | 192.168.0.15 | 192.168.0.1 – 192.168.0.14 |
Usable addresses in the cloud
Cloud providers reserve a few addresses in every subnet for the router, DNS and future use, so the usable count is lower than the formula gives.
| Provider | Usable in a /28 | Notes |
|---|---|---|
| AWS VPC subnet | 11 | Allowed (/16 to /28). AWS reserves the first four addresses and the last one. |
| Azure virtual network subnet | 11 | Allowed. Azure reserves the first four addresses and the last one. |
| Google Cloud subnet | 12 | Allowed. Google Cloud reserves the first two and the last two addresses. |
How the numbers are derived
An IPv4 address has 32 bits. A /28 uses 28 of them for the network, leaving 4 host bits, so the block has 24 = 16 addresses. The first address (all host bits 0) is the network address and the last (all host bits 1) is the broadcast address, which leaves 14 for hosts. The subnet mask is 28 ones followed by 4 zeros, written in dotted decimal as 255.255.255.240; the wildcard mask 0.0.0.15 is its inverse, used in Cisco ACLs and OSPF configuration.
FAQ
How many hosts can a /28 have?
16 addresses in total, of which 14 are usable after removing the network and broadcast addresses. Cloud providers reserve a few more: 11 usable in AWS and Azure, 12 in Google Cloud.
How many /28 subnets fit in a /24?
16. A /24 has 256 addresses and a /28 has 16, so 256 ÷ 16 = 16 blocks.