Last reviewed: May 2026
A /18 subnet uses 18 bits for the network portion of an IPv4 address, leaving 14 bits for host addressing. This produces 16,384 total IP addresses and 16,382 usable hosts. A /18 sits between the common /16 and /20, making it useful for large regional allocations and multi-site enterprise networks that need more than a /20 but don't require a full /16.
Calculate any /18 subnet instantly →| Property | Value |
|---|---|
| Prefix length | /18 |
| Subnet mask | 255.255.192.0 |
| Wildcard mask | 0.0.63.255 |
| Total addresses | 16,384 |
| Usable host addresses | 16,382 |
| Network address | x.x.x.0 (third octet must be multiple of 64: .0, .64, .128, .192) |
| Broadcast address | x.x.63.255 |
| Binary mask | 11111111.11111111.11000000.00000000 |
| AWS usable hosts | 16,379 (AWS reserves 5 IPs per subnet) |
A /18 divides a /16 into exactly 4 equal blocks — third octets .0–.63, .64–.127, .128–.191, and .192–.255. This makes /18 a clean way to partition a /16 into four large zones: for example, splitting a VPC into four regions or business units, each getting their own /18 super-block to subdivide as they see fit.
| Subnet | Range | Third-Octet Span | Contains /24s |
|---|---|---|---|
| 10.0.0.0/18 | 10.0.0.0 – 10.0.63.255 | .0–.63 | 64 |
| 10.0.64.0/18 | 10.0.64.0 – 10.0.127.255 | .64–.127 | 64 |
| 10.0.128.0/18 | 10.0.128.0 – 10.0.191.255 | .128–.191 | 64 |
| 10.0.192.0/18 | 10.0.192.0 – 10.0.255.255 | .192–.255 | 64 |
| Subnet Size | Number in a /18 | Usable Hosts Each |
|---|---|---|
| /20 | 4 | 4,094 |
| /22 | 16 | 1,022 |
| /24 | 64 | 254 |
| /26 | 256 | 62 |
| /28 | 1,024 | 14 |
| CIDR | Subnet Mask | Total IPs | Usable Hosts | AWS Usable | Typical Use |
|---|---|---|---|---|---|
| /16 | 255.255.0.0 | 65,536 | 65,534 | 65,531 | VPC root CIDR |
| /18 | 255.255.192.0 | 16,384 | 16,382 | 16,379 | Large regional block, multi-campus |
| /20 | 255.255.240.0 | 4,096 | 4,094 | 4,091 | EKS node groups, large AZ subnets |
| /22 | 255.255.252.0 | 1,024 | 1,022 | 1,019 | Large office VLAN |
| /24 | 255.255.255.0 | 256 | 254 | 251 | Standard workload subnet |
A /18 subnet has 16,382 usable host addresses from a total of 16,384 IPs. Two addresses are reserved: the network address and the broadcast address. In AWS, 16,379 IPs are usable after the 5 reserved addresses are subtracted.
A /18 block contains 64 subnets of /24 size (2^(24-18) = 2^6 = 64). It also contains 16 subnets of /22 size, or 4 subnets of /20 size.
The subnet mask for a /18 network is 255.255.192.0. In binary, 18 bits are set to 1 followed by 14 bits of 0: 11111111.11111111.11000000.00000000.