/3 vs /7 — Subnet Comparison
A /3 subnet is 16× larger than a /7. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /3 has 24 = 16 times as many addresses.
Key Differences
How 16 /7 Subnets Divide a /3
Example using 10.0.0.0/3 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 0.0.0.0/7 | 0.0.0.0 | 0.0.0.1 | 1.255.255.254 | 1.255.255.255 | 33,554,430 |
| 2 | 2.0.0.0/7 | 2.0.0.0 | 2.0.0.1 | 3.255.255.254 | 3.255.255.255 | 33,554,430 |
| 3 | 4.0.0.0/7 | 4.0.0.0 | 4.0.0.1 | 5.255.255.254 | 5.255.255.255 | 33,554,430 |
| 4 | 6.0.0.0/7 | 6.0.0.0 | 6.0.0.1 | 7.255.255.254 | 7.255.255.255 | 33,554,430 |
| 5 | 8.0.0.0/7 | 8.0.0.0 | 8.0.0.1 | 9.255.255.254 | 9.255.255.255 | 33,554,430 |
| 6 | 10.0.0.0/7 | 10.0.0.0 | 10.0.0.1 | 11.255.255.254 | 11.255.255.255 | 33,554,430 |
| 7 | 12.0.0.0/7 | 12.0.0.0 | 12.0.0.1 | 13.255.255.254 | 13.255.255.255 | 33,554,430 |
| 8 | 14.0.0.0/7 | 14.0.0.0 | 14.0.0.1 | 15.255.255.254 | 15.255.255.255 | 33,554,430 |
| 9 | 16.0.0.0/7 | 16.0.0.0 | 16.0.0.1 | 17.255.255.254 | 17.255.255.255 | 33,554,430 |
| 10 | 18.0.0.0/7 | 18.0.0.0 | 18.0.0.1 | 19.255.255.254 | 19.255.255.255 | 33,554,430 |
| 11 | 20.0.0.0/7 | 20.0.0.0 | 20.0.0.1 | 21.255.255.254 | 21.255.255.255 | 33,554,430 |
| 12 | 22.0.0.0/7 | 22.0.0.0 | 22.0.0.1 | 23.255.255.254 | 23.255.255.255 | 33,554,430 |
| 13 | 24.0.0.0/7 | 24.0.0.0 | 24.0.0.1 | 25.255.255.254 | 25.255.255.255 | 33,554,430 |
| 14 | 26.0.0.0/7 | 26.0.0.0 | 26.0.0.1 | 27.255.255.254 | 27.255.255.255 | 33,554,430 |
| 15 | 28.0.0.0/7 | 28.0.0.0 | 28.0.0.1 | 29.255.255.254 | 29.255.255.255 | 33,554,430 |
| 16 | 30.0.0.0/7 | 30.0.0.0 | 30.0.0.1 | 31.255.255.254 | 31.255.255.255 | 33,554,430 |
FAQ
What is the difference between /3 and /7?
A /3 has 536,870,910 usable hosts
and a /7 has 33,554,430.
The subnet masks differ: /3 uses 224.0.0.0
while /7 uses 254.0.0.0.
Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means
/3 is exactly 16× larger.
How many /7 subnets fit in a /3?
Exactly 16 /7 subnets fit perfectly inside one /3 with no wasted space. To split a /3 into /7s, 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.