/20 Subnet: Mask 255.255.240.0, 4,094 Usable Hosts
A /20 subnet has a subnet mask of 255.255.240.0 and contains 4,096 total IP addresses, of which 4,094 are usable host addresses (the network and broadcast addresses are reserved). A /20 contains 16 /24 networks.
| CIDR notation | /20 |
|---|---|
| Subnet mask | 255.255.240.0 |
| Wildcard mask | 0.0.15.255 |
| Mask in binary | 11111111.11111111.11110000.00000000 |
| Total addresses | 4,096 (2^12) |
| Usable hosts | 4,094 |
| Host bits | 12 |
Usable hosts in a /20 by platform
Cloud providers reserve more than the usual two addresses per subnet, so the same /20 gives you fewer usable IPs in the cloud than on a standard LAN.
| Platform | Reserved IPs | Usable hosts |
|---|---|---|
| Standard (network + broadcast) | 2 | 4,094 |
| AWS VPC | 5 | 4,091 |
| Microsoft Azure VNet | 5 | 4,091 |
| Google Cloud VPC | 4 | 4,092 |
| Oracle Cloud VCN | 3 | 4,093 |
Good to know
A /20 (4,096 addresses) is a common size for a cloud VPC or a campus building, big enough to split into many subnets without being wasteful.
How a /20 is calculated
- The /20 means the first 20 bits are the network portion, leaving 12 host bits.
- Total addresses = 2^(32 - 20) = 2^12 = 4,096.
- Usable hosts (standard) = 4,096 - 2 (network + broadcast) = 4,094.
- Subnet mask = 255.255.240.0; wildcard mask = 0.0.15.255.
Want to split a /20 into smaller subnets, see every address range, or plan a VLSM layout? Open the free subnet calculator →