IPRangeExplorer

/18 vs /19 — Subnet Comparison

A /18 subnet is 2× larger than a /19. Every additional bit in the prefix halves the address space — the 1-bit difference between these two means /18 has 21 = 2 times as many addresses.

/18

16K IPs — quarter of a /16

Full reference →
Total IPs 16,384
Usable Hosts 16,382
Subnet Mask 255.255.192.0
Wildcard Mask 0.0.63.255

Typical Uses

  • →VPC tier segmentation
  • →Large-office building network
/19
Full reference →
Total IPs 8,192
Usable Hosts 8,190
Subnet Mask 255.255.224.0
Wildcard Mask 0.0.31.255

Key Differences

2×
more IPs in /18 than /19
2
/19 subnets fit inside one /18
1
bit of difference in prefix length

How 2 /19 Subnets Divide a /18

Example using 10.0.0.0/18 as the parent block.

# CIDR Network First Usable Last Usable Broadcast Hosts
1 10.0.0.0/19 10.0.0.0 10.0.0.1 10.0.31.254 10.0.31.255 8,190
2 10.0.32.0/19 10.0.32.0 10.0.32.1 10.0.63.254 10.0.63.255 8,190

FAQ

What is the difference between /18 and /19?

A /18 has 16,382 usable hosts and a /19 has 8,190. The subnet masks differ: /18 uses 255.255.192.0 while /19 uses 255.255.224.0. Every additional bit in the prefix halves the number of addresses — so the 1-bit gap means /18 is exactly 2× larger.

How many /19 subnets fit in a /18?

Exactly 2 /19 subnets fit perfectly inside one /18 with no wasted space. To split a /18 into /19s, 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.