/9 vs /10 — Subnet Comparison
A /9 subnet is 2× larger than a /10. Every additional bit in the prefix halves the address space — the 1-bit difference between these two means /9 has 21 = 2 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
4 million IPs — quarter of a /8
Typical Uses
- →Major regional segment in enterprise
- →Large cloud region allocation
Key Differences
How 2 /10 Subnets Divide a /9
Example using 10.0.0.0/9 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/10 | 10.0.0.0 | 10.0.0.1 | 10.63.255.254 | 10.63.255.255 | 4,194,302 |
| 2 | 10.64.0.0/10 | 10.64.0.0 | 10.64.0.1 | 10.127.255.254 | 10.127.255.255 | 4,194,302 |
FAQ
What is the difference between /9 and /10?
A /9 has 8,388,606 usable hosts
and a /10 has 4,194,302.
The subnet masks differ: /9 uses 255.128.0.0
while /10 uses 255.192.0.0.
Every additional bit in the prefix halves the number of addresses — so the 1-bit gap means
/9 is exactly 2× larger.
How many /10 subnets fit in a /9?
Exactly 2 /10 subnets fit perfectly inside one /9 with no wasted space. To split a /9 into /10s, just increment the last 1 bit of the network address for each new subnet.
Which should I choose?
/9 is typically used for: Large regional allocations. /10 is better for: Enterprise regional segment. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.