The /12 subnet
A /12 subnet uses the mask 255.240.0.0 and holds 1,048,576 addresses, 1,048,574 of them usable.
A /12 is a large network of 1,048,576 addresses, 1,048,574 of them usable, with the mask 255.240.0.0. It is bigger than most single sites need and is usually subdivided.
Address plans use a /12 as a site-level or campus-level supernet, then split it into /24s or smaller per VLAN. The wildcard 0.15.255.255 matches the whole block in an access list.
Below you can see the exact network, broadcast, and host range for any /12 you enter, calculated instantly in your browser.
Calculate a /12 network
Accepts CIDR (192.0.2.0/24), IP + mask (192.0.2.0 255.255.255.0), or a bare IP (defaults to /24).
10101100.00010000.00000000.0000000011111111.11110000.00000000.00000000Example: 172.16.0.0/12
Taking 172.16.0.0/12 as a worked example, the block breaks down like this:
| Network address | 172.16.0.0 |
|---|---|
| Usable range | 172.16.0.1 - 172.31.255.254 |
| Broadcast address | 172.31.255.255 |
| Total addresses | 1,048,576 |
| Usable hosts | 1,048,574 |
| Size | 16 class B blocks |
Frequently asked questions
What is the subnet mask for a /12?
A /12 uses the subnet mask 255.240.0.0. Its wildcard mask, used in access lists, is 0.15.255.255.
How many hosts are in a /12 subnet?
A /12 has 1,048,576 total addresses and 1,048,574 usable hosts (the total minus the network and broadcast addresses, except for /31 and /32).
What is a /12 used for?
Large network. It is equivalent to 16 class B blocks.
How do I calculate a /12 network?
Set the host bits to zero for the network address and to one for the broadcast address. The calculator on this page does it for any /12 block you enter.