The /28 subnet, explained
Everything about a /28 CIDR block — mask, address count, usable hosts and where a /28 fits in real network plans.
| Prefix length | /28 — 28 network bits, 4 host bits |
| Subnet mask | 255.255.255.240 |
| Wildcard (ACL) mask | 0.0.0.15 |
| Binary mask | 11111111.11111111.11111111.11110000 |
| Total addresses | 2^4 = 16 |
| Usable hosts | 14 (total − network − broadcast) |
| A /16 holds | 4,096 × /28 subnets |
| Example block | 192.168.1.0/28 |
Notes
A /28 prefix means the first 28 bits of the 32-bit IPv4 address identify the network and the remaining 4 bits identify hosts — giving 2^4 = 16 addresses. The first address (network) and the last (broadcast) are not assignable in a standard subnet.
Cloud sizing: a /28 is valid as an AWS VPC (allowed range /16–/28). AWS reserves 5 addresses per subnet, so a /28 subnet gives 11 assignable IPs there; GCP reserves 4 (12 assignable).
Adjacent sizes: /8 · /9 · /10 · /11 · /12 · /13 · /14 · /15 · /16 · /17 · /18 · /19 · /20 · /21 · /22 · /23 · /24 · /25 · /26 · /27 · /29 · /30 · /31 · /32
Frequently asked questions
How many IP addresses are in a /28?
16 total addresses, of which 14 are usable hosts (network and broadcast addresses are reserved).
What is the subnet mask for /28?
255.255.255.240 (wildcard mask 0.0.0.15).
What does /28 mean in an IP address?
The /28 suffix is CIDR notation: the first 28 bits are the network part, the last 4 bits are the host part.