The /18 subnet
A /18 subnet uses the mask 255.255.192.0 and holds 16,384 addresses, 16,382 of them usable.
A /18 sits between a /16 and a /24: 16,384 addresses, 16,382 usable, mask 255.255.192.0. It is a common size for a large flat segment or for aggregating several /24s into one route.
Summarizing contiguous /24s into a /18 keeps routing tables small. The block still fits inside a single broadcast domain if you want it to, though most designs subnet it further.
Below you can see the exact network, broadcast, and host range for any /18 you enter, calculated instantly in your browser.
Calculate a /18 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).
11000000.00000000.00000010.0000000011111111.11111111.11000000.00000000Example: 192.0.2.0/18
Taking 192.0.2.0/18 as a worked example, the block breaks down like this:
| Network address | 192.0.0.0 |
|---|---|
| Usable range | 192.0.0.1 - 192.0.63.254 |
| Broadcast address | 192.0.63.255 |
| Total addresses | 16,384 |
| Usable hosts | 16,382 |
| Size | 64 class C blocks |
Frequently asked questions
What is the subnet mask for a /18?
A /18 uses the subnet mask 255.255.192.0. Its wildcard mask, used in access lists, is 0.0.63.255.
How many hosts are in a /18 subnet?
A /18 has 16,384 total addresses and 16,382 usable hosts (the total minus the network and broadcast addresses, except for /31 and /32).
What is a /18 used for?
Standard LAN size. It is equivalent to 64 class C blocks.
How do I calculate a /18 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 /18 block you enter.