/12 vs /16 — Subnet Comparison
A /12 subnet is 16× larger than a /16. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /12 has 24 = 16 times as many addresses.
1 million IPs — the 172.16/12 range
Typical Uses
- →RFC 1918 Class B private range (172.16.0.0/12)
- →Large enterprise segments
65K IPs — standard VPC or site block
Typical Uses
- →AWS / Azure VPC or VNet CIDR
- →Enterprise campus or data centre segment
- →Docker overlay network
Key Differences
How 16 /16 Subnets Divide a /12
Example using 10.0.0.0/12 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/16 | 10.0.0.0 | 10.0.0.1 | 10.0.255.254 | 10.0.255.255 | 65,534 |
| 2 | 10.1.0.0/16 | 10.1.0.0 | 10.1.0.1 | 10.1.255.254 | 10.1.255.255 | 65,534 |
| 3 | 10.2.0.0/16 | 10.2.0.0 | 10.2.0.1 | 10.2.255.254 | 10.2.255.255 | 65,534 |
| 4 | 10.3.0.0/16 | 10.3.0.0 | 10.3.0.1 | 10.3.255.254 | 10.3.255.255 | 65,534 |
| 5 | 10.4.0.0/16 | 10.4.0.0 | 10.4.0.1 | 10.4.255.254 | 10.4.255.255 | 65,534 |
| 6 | 10.5.0.0/16 | 10.5.0.0 | 10.5.0.1 | 10.5.255.254 | 10.5.255.255 | 65,534 |
| 7 | 10.6.0.0/16 | 10.6.0.0 | 10.6.0.1 | 10.6.255.254 | 10.6.255.255 | 65,534 |
| 8 | 10.7.0.0/16 | 10.7.0.0 | 10.7.0.1 | 10.7.255.254 | 10.7.255.255 | 65,534 |
| 9 | 10.8.0.0/16 | 10.8.0.0 | 10.8.0.1 | 10.8.255.254 | 10.8.255.255 | 65,534 |
| 10 | 10.9.0.0/16 | 10.9.0.0 | 10.9.0.1 | 10.9.255.254 | 10.9.255.255 | 65,534 |
| 11 | 10.10.0.0/16 | 10.10.0.0 | 10.10.0.1 | 10.10.255.254 | 10.10.255.255 | 65,534 |
| 12 | 10.11.0.0/16 | 10.11.0.0 | 10.11.0.1 | 10.11.255.254 | 10.11.255.255 | 65,534 |
| 13 | 10.12.0.0/16 | 10.12.0.0 | 10.12.0.1 | 10.12.255.254 | 10.12.255.255 | 65,534 |
| 14 | 10.13.0.0/16 | 10.13.0.0 | 10.13.0.1 | 10.13.255.254 | 10.13.255.255 | 65,534 |
| 15 | 10.14.0.0/16 | 10.14.0.0 | 10.14.0.1 | 10.14.255.254 | 10.14.255.255 | 65,534 |
| 16 | 10.15.0.0/16 | 10.15.0.0 | 10.15.0.1 | 10.15.255.254 | 10.15.255.255 | 65,534 |
FAQ
What is the difference between /12 and /16?
A /12 has 1,048,574 usable hosts
and a /16 has 65,534.
The subnet masks differ: /12 uses 255.240.0.0
while /16 uses 255.255.0.0.
Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means
/12 is exactly 16× larger.
How many /16 subnets fit in a /12?
Exactly 16 /16 subnets fit perfectly inside one /12 with no wasted space. To split a /12 into /16s, just increment the last 4 bits of the network address for each new subnet.
Which should I choose?
/12 is typically used for: RFC 1918 Class B range. /16 is better for: Cloud VPC CIDR, campus network. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.