CIDR Notation Calculator
CIDR Block Details
Get full details for a CIDR notation block
Hosts to CIDR
Find the smallest CIDR block that fits a given number of hosts
Formula
Usable Hosts = 2^(32-CIDR) - 2 | Total Addresses = 2^(32-CIDR)
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated network mask. Written as IP/prefix (e.g., 192.168.1.0/24), the prefix indicates how many leading bits define the network portion. It replaced classful addressing to allow more flexible allocation of IP addresses.
How do I choose the right CIDR block?
Choose the smallest CIDR block that fits your required hosts. For 100 hosts, /25 gives 126 usable. For 500 hosts, /23 gives 510 usable. Always plan for growth -- typically allocate 20-50% more addresses than currently needed.
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