A /20 holds 4,096 addresses (4,094 usable) with the mask 255.255.240.0. It’s the size AWS gives each subnet in a default VPC, one per availability zone. Note that AWS reserves five addresses in every subnet, so a /20 there gives you 4,091. The third octet steps in blocks of 16.
Facts
- Prefix
- /20
- Subnet mask
- 255.255.240.0
- Wildcard mask
- 0.0.15.255
- Binary mask
- 11111111.11111111.11110000.00000000
- Total addresses
- 4,096
- Usable hosts
- 4,094
- Example range
- 192.168.0.0/20: 192.168.0.0 – 192.168.15.255
- Typical use
- Campus networks; AWS default VPC subnets are /20.
Try it
Try: , ,
- CIDR block
- 192.168.0.0/20
- IP range
- 192.168.0.0 – 192.168.15.255
- Addresses
- 4,096
- Usable hosts
- 4,094
- Subnet mask
- 255.255.240.0
- Wildcard mask
- 0.0.15.255
Frequently asked questions
How many hosts are in a /20?
A /20 has 4,096 addresses. Subtracting the network and broadcast addresses leaves 4,094 usable hosts.
What is the subnet mask for /20?
/20 is 255.255.240.0 (wildcard mask 0.0.15.255). In binary that’s 20 ones followed by 12 zeros.