CIDR Calculator

Convert CIDR notation to IP address ranges.

Format: IP/prefix (e.g., 192.168.0.0/24)

IP Range
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Network
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Broadcast
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Subnet Mask
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Total Addresses
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Binary Mask
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What is CIDR Notation?

CIDR (Classless Inter-Domain Routing) was introduced in 1993 to replace the old classful networking system (Class A, B, C) which wasted IP address space. CIDR allows network boundaries to be placed at any bit position, not just at the 8, 16, or 24 bit marks. This flexibility enables more efficient allocation of IP addresses and reduces the size of routing tables.

A CIDR block is written as an IP address followed by a slash and a prefix length (e.g., 10.0.0.0/8). The prefix length tells you how many leading bits are fixed (the network part). The remaining bits are available for host addresses. This tool calculates all derived values from any CIDR block: the IP range, network and broadcast addresses, subnet mask, and total number of addresses.

Common CIDR Blocks

/8

16,777,216 addresses

Class A network

/16

65,536 addresses

Class B network

/24

256 addresses

Class C network

/32

1 address

Single host

Private IP Ranges (RFC 1918)

Frequently Asked Questions

What is the difference between CIDR calculator and subnet calculator?
They are closely related tools. A CIDR calculator takes a CIDR block (like 10.0.0.0/8) and shows the IP range, while a subnet calculator takes an IP and prefix and shows detailed subnet information including usable hosts, first/last host, and wildcard mask. Our Subnet Calculator provides the more detailed breakdown.
How do I use CIDR in AWS security groups?
AWS security groups use CIDR notation to define allowed IP ranges. Use 0.0.0.0/0 for all IPv4 addresses (public access), 10.0.0.0/16 for your VPC range, or a specific IP like 203.0.113.50/32 for a single host. For IPv6, use ::/0 for all addresses.
What does /32 mean in CIDR?
A /32 CIDR block represents a single IP address. All 32 bits are the network portion, leaving zero bits for hosts. It is commonly used in firewall rules and security groups to allow or deny a specific IP address. For example, 192.168.1.100/32 refers to exactly one address: 192.168.1.100.
Can I aggregate multiple CIDR blocks?
Yes, this is called CIDR aggregation or supernetting. Two adjacent /24 blocks can be combined into a /23, two /23 blocks into a /22, and so on. For example, 192.168.0.0/24 and 192.168.1.0/24 can be aggregated into 192.168.0.0/23. This only works when the blocks are contiguous and properly aligned on the boundary.

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