/3 vs /4 — Subnet Comparison
A /3 subnet is 2× larger than a /4. Every additional bit in the prefix halves the address space — the 1-bit difference between these two means /3 has 21 = 2 times as many addresses.
Key Differences
How 2 /4 Subnets Divide a /3
Example using 10.0.0.0/3 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 0.0.0.0/4 | 0.0.0.0 | 0.0.0.1 | 15.255.255.254 | 15.255.255.255 | 268,435,454 |
| 2 | 16.0.0.0/4 | 16.0.0.0 | 16.0.0.1 | 31.255.255.254 | 31.255.255.255 | 268,435,454 |
FAQ
What is the difference between /3 and /4?
A /3 has 536,870,910 usable hosts
and a /4 has 268,435,454.
The subnet masks differ: /3 uses 224.0.0.0
while /4 uses 240.0.0.0.
Every additional bit in the prefix halves the number of addresses — so the 1-bit gap means
/3 is exactly 2× larger.
How many /4 subnets fit in a /3?
Exactly 2 /4 subnets fit perfectly inside one /3 with no wasted space. To split a /3 into /4s, 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.