/16 vs /18 — Subnet Comparison
A /16 subnet is 4× larger than a /18. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /16 has 22 = 4 times as many addresses.
65K IPs — standard VPC or site block
Typical Uses
- →AWS / Azure VPC or VNet CIDR
- →Enterprise campus or data centre segment
- →Docker overlay network
16K IPs — quarter of a /16
Typical Uses
- →VPC tier segmentation
- →Large-office building network
Key Differences
How 4 /18 Subnets Divide a /16
Example using 10.0.0.0/16 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/18 | 10.0.0.0 | 10.0.0.1 | 10.0.63.254 | 10.0.63.255 | 16,382 |
| 2 | 10.0.64.0/18 | 10.0.64.0 | 10.0.64.1 | 10.0.127.254 | 10.0.127.255 | 16,382 |
| 3 | 10.0.128.0/18 | 10.0.128.0 | 10.0.128.1 | 10.0.191.254 | 10.0.191.255 | 16,382 |
| 4 | 10.0.192.0/18 | 10.0.192.0 | 10.0.192.1 | 10.0.255.254 | 10.0.255.255 | 16,382 |
FAQ
What is the difference between /16 and /18?
A /16 has 65,534 usable hosts
and a /18 has 16,382.
The subnet masks differ: /16 uses 255.255.0.0
while /18 uses 255.255.192.0.
Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means
/16 is exactly 4× larger.
How many /18 subnets fit in a /16?
Exactly 4 /18 subnets fit perfectly inside one /16 with no wasted space. To split a /16 into /18s, just increment the last 2 bits of the network address for each new subnet.
Which should I choose?
/16 is typically used for: Cloud VPC CIDR, campus network. /18 is better for: VPC segment. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.