/8 vs /12 — Subnet Comparison
A /8 subnet is 16× larger than a /12. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /8 has 24 = 16 times as many addresses.
16 million IPs — Class A network
Typical Uses
- →Entire Class A private range (10.0.0.0/8)
- →Large ISP or carrier allocations
- →Enterprise-wide addressing plan
1 million IPs — the 172.16/12 range
Typical Uses
- →RFC 1918 Class B private range (172.16.0.0/12)
- →Large enterprise segments
Key Differences
How 16 /12 Subnets Divide a /8
Example using 10.0.0.0/8 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/12 | 10.0.0.0 | 10.0.0.1 | 10.15.255.254 | 10.15.255.255 | 1,048,574 |
| 2 | 10.16.0.0/12 | 10.16.0.0 | 10.16.0.1 | 10.31.255.254 | 10.31.255.255 | 1,048,574 |
| 3 | 10.32.0.0/12 | 10.32.0.0 | 10.32.0.1 | 10.47.255.254 | 10.47.255.255 | 1,048,574 |
| 4 | 10.48.0.0/12 | 10.48.0.0 | 10.48.0.1 | 10.63.255.254 | 10.63.255.255 | 1,048,574 |
| 5 | 10.64.0.0/12 | 10.64.0.0 | 10.64.0.1 | 10.79.255.254 | 10.79.255.255 | 1,048,574 |
| 6 | 10.80.0.0/12 | 10.80.0.0 | 10.80.0.1 | 10.95.255.254 | 10.95.255.255 | 1,048,574 |
| 7 | 10.96.0.0/12 | 10.96.0.0 | 10.96.0.1 | 10.111.255.254 | 10.111.255.255 | 1,048,574 |
| 8 | 10.112.0.0/12 | 10.112.0.0 | 10.112.0.1 | 10.127.255.254 | 10.127.255.255 | 1,048,574 |
| 9 | 10.128.0.0/12 | 10.128.0.0 | 10.128.0.1 | 10.143.255.254 | 10.143.255.255 | 1,048,574 |
| 10 | 10.144.0.0/12 | 10.144.0.0 | 10.144.0.1 | 10.159.255.254 | 10.159.255.255 | 1,048,574 |
| 11 | 10.160.0.0/12 | 10.160.0.0 | 10.160.0.1 | 10.175.255.254 | 10.175.255.255 | 1,048,574 |
| 12 | 10.176.0.0/12 | 10.176.0.0 | 10.176.0.1 | 10.191.255.254 | 10.191.255.255 | 1,048,574 |
| 13 | 10.192.0.0/12 | 10.192.0.0 | 10.192.0.1 | 10.207.255.254 | 10.207.255.255 | 1,048,574 |
| 14 | 10.208.0.0/12 | 10.208.0.0 | 10.208.0.1 | 10.223.255.254 | 10.223.255.255 | 1,048,574 |
| 15 | 10.224.0.0/12 | 10.224.0.0 | 10.224.0.1 | 10.239.255.254 | 10.239.255.255 | 1,048,574 |
| 16 | 10.240.0.0/12 | 10.240.0.0 | 10.240.0.1 | 10.255.255.254 | 10.255.255.255 | 1,048,574 |
FAQ
What is the difference between /8 and /12?
A /8 has 16,777,214 usable hosts
and a /12 has 1,048,574.
The subnet masks differ: /8 uses 255.0.0.0
while /12 uses 255.240.0.0.
Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means
/8 is exactly 16× larger.
How many /12 subnets fit in a /8?
Exactly 16 /12 subnets fit perfectly inside one /8 with no wasted space. To split a /8 into /12s, just increment the last 4 bits of the network address for each new subnet.
Which should I choose?
/8 is typically used for: Entire private Class A or ISP allocation. /12 is better for: RFC 1918 Class B range. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.