/12 Subnet: Mask 255.240.0.0, 1,048,574 Usable Hosts

A /12 subnet has a subnet mask of 255.240.0.0 and contains 1,048,576 total IP addresses, of which 1,048,574 are usable host addresses (the network and broadcast addresses are reserved). A /12 contains 4,096 /24 networks.

Usable hosts in a /12 by platform

Cloud providers reserve more than the usual two addresses per subnet, so the same /12 gives you fewer usable IPs in the cloud than on a standard LAN.

Good to know

A /12 is the size of the 172.16.0.0/12 private range (RFC 1918), the middle of the three private blocks and a common pick for mid-size networks.

How a /12 is calculated

• The /12 means the first 12 bits are the network portion, leaving 20 host bits.
• Total addresses = 2^(32 - 12) = 2^20 = 1,048,576.
• Usable hosts (standard) = 1,048,576 - 2 (network + broadcast) = 1,048,574.
• Subnet mask = 255.240.0.0; wildcard mask = 0.15.255.255.