/16 vs /20 — Subnet Comparison
A /16 subnet is 16× larger than a /20. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /16 has 24 = 16 times as many addresses.
65K IPs — standard VPC or site block
Typical Uses
- →AWS / Azure VPC or VNet CIDR
- →Enterprise campus or data centre segment
- →Docker overlay network
4K IPs — AWS default subnet size
Typical Uses
- →AWS default subnet (per AZ)
- →Medium-large application tier subnet
- →Office floor VLAN
Key Differences
How 16 /20 Subnets Divide a /16
Example using 10.0.0.0/16 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/20 | 10.0.0.0 | 10.0.0.1 | 10.0.15.254 | 10.0.15.255 | 4,094 |
| 2 | 10.0.16.0/20 | 10.0.16.0 | 10.0.16.1 | 10.0.31.254 | 10.0.31.255 | 4,094 |
| 3 | 10.0.32.0/20 | 10.0.32.0 | 10.0.32.1 | 10.0.47.254 | 10.0.47.255 | 4,094 |
| 4 | 10.0.48.0/20 | 10.0.48.0 | 10.0.48.1 | 10.0.63.254 | 10.0.63.255 | 4,094 |
| 5 | 10.0.64.0/20 | 10.0.64.0 | 10.0.64.1 | 10.0.79.254 | 10.0.79.255 | 4,094 |
| 6 | 10.0.80.0/20 | 10.0.80.0 | 10.0.80.1 | 10.0.95.254 | 10.0.95.255 | 4,094 |
| 7 | 10.0.96.0/20 | 10.0.96.0 | 10.0.96.1 | 10.0.111.254 | 10.0.111.255 | 4,094 |
| 8 | 10.0.112.0/20 | 10.0.112.0 | 10.0.112.1 | 10.0.127.254 | 10.0.127.255 | 4,094 |
| 9 | 10.0.128.0/20 | 10.0.128.0 | 10.0.128.1 | 10.0.143.254 | 10.0.143.255 | 4,094 |
| 10 | 10.0.144.0/20 | 10.0.144.0 | 10.0.144.1 | 10.0.159.254 | 10.0.159.255 | 4,094 |
| 11 | 10.0.160.0/20 | 10.0.160.0 | 10.0.160.1 | 10.0.175.254 | 10.0.175.255 | 4,094 |
| 12 | 10.0.176.0/20 | 10.0.176.0 | 10.0.176.1 | 10.0.191.254 | 10.0.191.255 | 4,094 |
| 13 | 10.0.192.0/20 | 10.0.192.0 | 10.0.192.1 | 10.0.207.254 | 10.0.207.255 | 4,094 |
| 14 | 10.0.208.0/20 | 10.0.208.0 | 10.0.208.1 | 10.0.223.254 | 10.0.223.255 | 4,094 |
| 15 | 10.0.224.0/20 | 10.0.224.0 | 10.0.224.1 | 10.0.239.254 | 10.0.239.255 | 4,094 |
| 16 | 10.0.240.0/20 | 10.0.240.0 | 10.0.240.1 | 10.0.255.254 | 10.0.255.255 | 4,094 |
FAQ
What is the difference between /16 and /20?
A /16 has 65,534 usable hosts
and a /20 has 4,094.
The subnet masks differ: /16 uses 255.255.0.0
while /20 uses 255.255.240.0.
Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means
/16 is exactly 16× larger.
How many /20 subnets fit in a /16?
Exactly 16 /20 subnets fit perfectly inside one /16 with no wasted space. To split a /16 into /20s, just increment the last 4 bits of the network address for each new subnet.
Which should I choose?
/16 is typically used for: Cloud VPC CIDR, campus network. /20 is better for: AWS default subnet, medium office VLAN. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.