/1 vs /3 — Subnet Comparison
A /1 subnet is 4× larger than a /3. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /1 has 22 = 4 times as many addresses.
Key Differences
How 4 /3 Subnets Divide a /1
Example using 10.0.0.0/1 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 0.0.0.0/3 | 0.0.0.0 | 0.0.0.1 | 31.255.255.254 | 31.255.255.255 | 536,870,910 |
| 2 | 32.0.0.0/3 | 32.0.0.0 | 32.0.0.1 | 63.255.255.254 | 63.255.255.255 | 536,870,910 |
| 3 | 64.0.0.0/3 | 64.0.0.0 | 64.0.0.1 | 95.255.255.254 | 95.255.255.255 | 536,870,910 |
| 4 | 96.0.0.0/3 | 96.0.0.0 | 96.0.0.1 | 127.255.255.254 | 127.255.255.255 | 536,870,910 |
FAQ
What is the difference between /1 and /3?
A /1 has 2,147,483,646 usable hosts
and a /3 has 536,870,910.
The subnet masks differ: /1 uses 128.0.0.0
while /3 uses 224.0.0.0.
Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means
/1 is exactly 4× larger.
How many /3 subnets fit in a /1?
Exactly 4 /3 subnets fit perfectly inside one /1 with no wasted space. To split a /1 into /3s, just increment the last 2 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.