/20 vs /24 — Subnet Comparison
A /20 subnet is 16× larger than a /24. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /20 has 24 = 16 times as many addresses.
4K IPs — AWS default subnet size
Typical Uses
- →AWS default subnet (per AZ)
- →Medium-large application tier subnet
- →Office floor VLAN
254 usable hosts — the industry standard
Typical Uses
- →Home and SOHO LAN (192.168.1.0/24)
- →Standard office VLAN
- →AWS/Azure subnet per AZ
Key Differences
How 16 /24 Subnets Divide a /20
Example using 10.0.0.0/20 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/24 | 10.0.0.0 | 10.0.0.1 | 10.0.0.254 | 10.0.0.255 | 254 |
| 2 | 10.0.1.0/24 | 10.0.1.0 | 10.0.1.1 | 10.0.1.254 | 10.0.1.255 | 254 |
| 3 | 10.0.2.0/24 | 10.0.2.0 | 10.0.2.1 | 10.0.2.254 | 10.0.2.255 | 254 |
| 4 | 10.0.3.0/24 | 10.0.3.0 | 10.0.3.1 | 10.0.3.254 | 10.0.3.255 | 254 |
| 5 | 10.0.4.0/24 | 10.0.4.0 | 10.0.4.1 | 10.0.4.254 | 10.0.4.255 | 254 |
| 6 | 10.0.5.0/24 | 10.0.5.0 | 10.0.5.1 | 10.0.5.254 | 10.0.5.255 | 254 |
| 7 | 10.0.6.0/24 | 10.0.6.0 | 10.0.6.1 | 10.0.6.254 | 10.0.6.255 | 254 |
| 8 | 10.0.7.0/24 | 10.0.7.0 | 10.0.7.1 | 10.0.7.254 | 10.0.7.255 | 254 |
| 9 | 10.0.8.0/24 | 10.0.8.0 | 10.0.8.1 | 10.0.8.254 | 10.0.8.255 | 254 |
| 10 | 10.0.9.0/24 | 10.0.9.0 | 10.0.9.1 | 10.0.9.254 | 10.0.9.255 | 254 |
| 11 | 10.0.10.0/24 | 10.0.10.0 | 10.0.10.1 | 10.0.10.254 | 10.0.10.255 | 254 |
| 12 | 10.0.11.0/24 | 10.0.11.0 | 10.0.11.1 | 10.0.11.254 | 10.0.11.255 | 254 |
| 13 | 10.0.12.0/24 | 10.0.12.0 | 10.0.12.1 | 10.0.12.254 | 10.0.12.255 | 254 |
| 14 | 10.0.13.0/24 | 10.0.13.0 | 10.0.13.1 | 10.0.13.254 | 10.0.13.255 | 254 |
| 15 | 10.0.14.0/24 | 10.0.14.0 | 10.0.14.1 | 10.0.14.254 | 10.0.14.255 | 254 |
| 16 | 10.0.15.0/24 | 10.0.15.0 | 10.0.15.1 | 10.0.15.254 | 10.0.15.255 | 254 |
FAQ
What is the difference between /20 and /24?
A /20 has 4,094 usable hosts
and a /24 has 254.
The subnet masks differ: /20 uses 255.255.240.0
while /24 uses 255.255.255.0.
Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means
/20 is exactly 16× larger.
How many /24 subnets fit in a /20?
Exactly 16 /24 subnets fit perfectly inside one /20 with no wasted space. To split a /20 into /24s, just increment the last 4 bits of the network address for each new subnet.
Which should I choose?
/20 is typically used for: AWS default subnet, medium office VLAN. /24 is better for: Standard subnet — home, office, cloud. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.