/10 vs /12 — Subnet Comparison

Q: What is the difference between /10 and /12?

A /10 subnet has 4,194,302 usable host addresses, while a /12 has 1,048,574. A /10 is 4× larger than a /12 — exactly 4 /12 subnets fit inside a single /10.

Q: How many /12 subnets fit in a /10?

Exactly 4 /12 subnets fit inside a /10. Each /12 has 1,048,574 usable hosts, and together they cover all 4,194,304 IP addresses in the /10.

A /10 subnet is 4× larger than a /12. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /10 has 2² = 4 times as many addresses.

/10

4 million IPs — quarter of a /8

Full reference →

Total IPs 4,194,304

Usable Hosts 4,194,302

Subnet Mask 255.192.0.0

Wildcard Mask 0.63.255.255

Typical Uses

→Major regional segment in enterprise
→Large cloud region allocation

/12

1 million IPs — the 172.16/12 range

Full reference →

Total IPs 1,048,576

Usable Hosts 1,048,574

Subnet Mask 255.240.0.0

Wildcard Mask 0.15.255.255

Typical Uses

→RFC 1918 Class B private range (172.16.0.0/12)
→Large enterprise segments

Key Differences

4×

more IPs in /10 than /12

/12 subnets fit inside one /10

bits of difference in prefix length

How 4 /12 Subnets Divide a /10

Example using 10.0.0.0/10 as the parent block.

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	10.0.0.0/12	10.0.0.0	10.0.0.1	10.15.255.254	10.15.255.255	1,048,574
2	10.16.0.0/12	10.16.0.0	10.16.0.1	10.31.255.254	10.31.255.255	1,048,574
3	10.32.0.0/12	10.32.0.0	10.32.0.1	10.47.255.254	10.47.255.255	1,048,574
4	10.48.0.0/12	10.48.0.0	10.48.0.1	10.63.255.254	10.63.255.255	1,048,574

FAQ

What is the difference between /10 and /12?

A /10 has 4,194,302 usable hosts and a /12 has 1,048,574. The subnet masks differ: /10 uses 255.192.0.0 while /12 uses 255.240.0.0. Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means /10 is exactly 4× larger.

How many /12 subnets fit in a /10?

Exactly 4 /12 subnets fit perfectly inside one /10 with no wasted space. To split a /10 into /12s, just increment the last 2 bits of the network address for each new subnet.

Which should I choose?

/10 is typically used for: Enterprise regional segment. /12 is better for: RFC 1918 Class B range. Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.