/15 vs /16 — Subnet Comparison
A /15 subnet is 2× larger than a /16. Every additional bit in the prefix halves the address space — the 1-bit difference between these two means /15 has 21 = 2 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
Key Differences
How 2 /16 Subnets Divide a /15
Example using 10.0.0.0/15 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 |
FAQ
What is the difference between /15 and /16?
A /15 has 131,070 usable hosts
and a /16 has 65,534.
The subnet masks differ: /15 uses 255.254.0.0
while /16 uses 255.255.0.0.
Every additional bit in the prefix halves the number of addresses — so the 1-bit gap means
/15 is exactly 2× larger.
How many /16 subnets fit in a /15?
Exactly 2 /16 subnets fit perfectly inside one /15 with no wasted space. To split a /15 into /16s, just increment the last 1 bit of the network address for each new subnet.
Which should I choose?
Choose based on how many hosts you need. Use the hosts → prefix calculator on the homepage to find the right size for your requirements.