/18 Subnet Mask ReferenceIPv4
A quarter of a /16, sixty-four /24s deep: <code>255.255.192.0</code> marks the /18, comfortable for 16,382 hosts. Manufacturing floors and hospital wings fit inside one with space left over.
/18 facts at a glance
- Subnet mask
- 255.255.192.0
- Wildcard mask
- 0.0.63.255
- Binary mask
- 11111111.11111111.11000000.00000000
- Total addresses
- 16,384
- Usable hosts
- 16,382 (excludes network & broadcast)
- Block size
- 16,384 addresses (214)
- Typical role
- Mid-size networks and ISP allocations
Example /18 networks
Three consecutive /18 blocks, starting at the /18 boundary that contains 198.51.100.0:
| Network | Usable range | Usable hosts |
|---|---|---|
| 198.51.64.0/18 | 198.51.64.1 – 198.51.127.254 | 16,382 |
| 198.51.128.0/18 | 198.51.128.1 – 198.51.191.254 | 16,382 |
| 198.51.192.0/18 | 198.51.192.1 – 198.51.255.254 | 16,382 |
How to calculate a /18 mask
A /18 mask sets the first 18 bits of a 32-bit number to 1 and leaves the remaining 14 bits as 0. In binary that reads 11111111.11111111.11000000.00000000, which converts to dotted decimal 255.255.192.0. Each block covers a contiguous run of 214 = 16,384 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 0.0.63.255.
Where /18 is used
- Single-building production and guest separation without touching the rest of a /16.
- Mid-size site cores that feed smaller /24 VLANs downstream.
- Starting blocks for VLSM plans mixing large and small departments.
Alignment rule: the third octet must sit on a multiple of 64. <code>10.1.64.0/18</code> spans 10.1.64.0 through 10.1.127.255.
Frequently asked questions
What is the subnet mask for /18?
<code>255.255.192.0</code>, wildcard <code>0.0.63.255</code>.
How many usable hosts does a /18 have?
16,382 of 16,384 total addresses.
How many /24s fit in a /18?
Sixty-four, stepping the third octet through its full range within one /18 block.
Open this block in a calculator
Open the /18 block in the subnet calculator