/5 vs /9 — Subnet Comparison
A /5 subnet is 16× larger than a /9. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /5 has 24 = 16 times as many addresses.
8.3 million IPs — half a /8
Typical Uses
- →Large regional ISP allocation
- →Half of a Class A block
- →Aggregated routing prefix
Key Differences
How 16 /9 Subnets Divide a /5
Example using 10.0.0.0/5 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 8.0.0.0/9 | 8.0.0.0 | 8.0.0.1 | 8.127.255.254 | 8.127.255.255 | 8,388,606 |
| 2 | 8.128.0.0/9 | 8.128.0.0 | 8.128.0.1 | 8.255.255.254 | 8.255.255.255 | 8,388,606 |
| 3 | 9.0.0.0/9 | 9.0.0.0 | 9.0.0.1 | 9.127.255.254 | 9.127.255.255 | 8,388,606 |
| 4 | 9.128.0.0/9 | 9.128.0.0 | 9.128.0.1 | 9.255.255.254 | 9.255.255.255 | 8,388,606 |
| 5 | 10.0.0.0/9 | 10.0.0.0 | 10.0.0.1 | 10.127.255.254 | 10.127.255.255 | 8,388,606 |
| 6 | 10.128.0.0/9 | 10.128.0.0 | 10.128.0.1 | 10.255.255.254 | 10.255.255.255 | 8,388,606 |
| 7 | 11.0.0.0/9 | 11.0.0.0 | 11.0.0.1 | 11.127.255.254 | 11.127.255.255 | 8,388,606 |
| 8 | 11.128.0.0/9 | 11.128.0.0 | 11.128.0.1 | 11.255.255.254 | 11.255.255.255 | 8,388,606 |
| 9 | 12.0.0.0/9 | 12.0.0.0 | 12.0.0.1 | 12.127.255.254 | 12.127.255.255 | 8,388,606 |
| 10 | 12.128.0.0/9 | 12.128.0.0 | 12.128.0.1 | 12.255.255.254 | 12.255.255.255 | 8,388,606 |
| 11 | 13.0.0.0/9 | 13.0.0.0 | 13.0.0.1 | 13.127.255.254 | 13.127.255.255 | 8,388,606 |
| 12 | 13.128.0.0/9 | 13.128.0.0 | 13.128.0.1 | 13.255.255.254 | 13.255.255.255 | 8,388,606 |
| 13 | 14.0.0.0/9 | 14.0.0.0 | 14.0.0.1 | 14.127.255.254 | 14.127.255.255 | 8,388,606 |
| 14 | 14.128.0.0/9 | 14.128.0.0 | 14.128.0.1 | 14.255.255.254 | 14.255.255.255 | 8,388,606 |
| 15 | 15.0.0.0/9 | 15.0.0.0 | 15.0.0.1 | 15.127.255.254 | 15.127.255.255 | 8,388,606 |
| 16 | 15.128.0.0/9 | 15.128.0.0 | 15.128.0.1 | 15.255.255.254 | 15.255.255.255 | 8,388,606 |
FAQ
What is the difference between /5 and /9?
A /5 has 134,217,726 usable hosts
and a /9 has 8,388,606.
The subnet masks differ: /5 uses 248.0.0.0
while /9 uses 255.128.0.0.
Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means
/5 is exactly 16× larger.
How many /9 subnets fit in a /5?
Exactly 16 /9 subnets fit perfectly inside one /5 with no wasted space. To split a /5 into /9s, just increment the last 4 bits 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.