CIDR Calculator

Category: Technology
- March 31, 2025
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Calculate network information based on IP address and subnet mask using CIDR notation. This calculator helps you determine network address, broadcast address, and available host ranges.

IP Address and Subnet

IP Address Entry
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Display Options

About CIDR Notation

CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing IP packets. It replaced the earlier addressing architecture of classful network design, which divided the address space into classes (A, B, C, D, E) with fixed sizes.

CIDR Notation Explained
  • Notation Format: CIDR uses a syntax of IP address followed by a slash and number (e.g., 192.168.1.0/24).
  • Prefix Length: The number after the slash represents the count of leading 1 bits in the subnet mask.
  • Address Range: A CIDR block specifies a contiguous range of IP addresses.
  • Subnet Mask: The subnet mask determines which portion of an IP address refers to the network and which portion refers to hosts.
Common CIDR Blocks
  • /8 (255.0.0.0): 16,777,214 hosts - Used for large organizations or regional internet registries
  • /16 (255.255.0.0): 65,534 hosts - Typical for large organizations
  • /24 (255.255.255.0): 254 hosts - Common for small networks and home LANs
  • /27 (255.255.255.224): 30 hosts - Useful for small office segments
  • /30 (255.255.255.252): 2 hosts - Typically used for point-to-point links
  • /32 (255.255.255.255): 1 host - Represents a single host
Private IP Address Ranges
  • 10.0.0.0/8: Class A private address range (10.0.0.0 to 10.255.255.255)
  • 172.16.0.0/12: Class B private address range (172.16.0.0 to 172.31.255.255)
  • 192.168.0.0/16: Class C private address range (192.168.0.0 to 192.168.255.255)
  • 169.254.0.0/16: Link-local addresses (automatic private IP addressing)

What Is a CIDR Calculator?

The CIDR Calculator is a simple tool that helps users analyze IP address details based on CIDR notation (Classless Inter-Domain Routing). It provides essential networking information, including the network address, broadcast address, and usable IP address range. Whether you're managing a home network or configuring enterprise-level routing, this tool offers clarity and precision in handling IP blocks.

Why Use a CIDR Calculator?

Understanding IP subnetting is critical for effective network planning, and the CIDR Calculator takes the guesswork out of it. Here's how it helps:

  • Quickly convert between CIDR notation and subnet mask.
  • Identify the range of usable IP addresses in a subnet.
  • Determine the network and broadcast addresses instantly.
  • See your IP address in binary or hexadecimal formats (optional).
  • Check the IP class and whether it belongs to a private, public, or special-use range.

How to Use the Calculator

Getting started is easy, even if you're not a networking expert:

  1. Enter an IP address (e.g., 192.168.1.1).
  2. Choose your input method: CIDR prefix (like /24) or a subnet mask (like 255.255.255.0).
  3. Click "Calculate Network Information".
  4. Review the output, including host range, total addresses, subnet mask, and more.
  5. Optionally, enable binary, hexadecimal, or classful details with the checkboxes.

Formula Used in the Calculator

Network Address:
Network = IP Address AND Subnet Mask

Broadcast Address:
Broadcast = Network Address OR Wildcard Mask

Usable Hosts:
Usable Hosts = 2^(32 - CIDR) - 2 (unless /31 or /32)

How This Calculator Is Useful

This tool is especially helpful for network administrators, students, and IT professionals who need to make informed decisions about IP address allocation and network segmentation. It's also useful when configuring routers, setting up VPNs, or troubleshooting network issues.

By converting and interpreting CIDR blocks accurately, the calculator ensures you're not wasting IP addresses and helps prevent configuration errors that could disrupt communication between devices.

Common Use Cases

  • Designing efficient subnet schemes for corporate networks.
  • Checking usable host IPs for specific subnet sizes.
  • Validating IP ranges for firewall or DHCP configuration.
  • Learning subnetting fundamentals for certification exams.

Frequently Asked Questions (FAQ)

What does CIDR stand for?

CIDR stands for Classless Inter-Domain Routing. It allows more flexible division of IP addresses than traditional class-based systems.

How is CIDR different from subnet masks?

CIDR uses a prefix length (e.g., /24) to define how many bits are used for the network part of the address. A subnet mask (e.g., 255.255.255.0) is another way to represent the same thing.

What is a broadcast address?

A broadcast address is the last address in a subnet. It's used to send messages to all devices within the same network segment.

What is a wildcard mask?

A wildcard mask is the inverse of a subnet mask. It's used in routing and firewall configurations to specify ranges of IP addresses.

Why are there fewer usable hosts than total addresses?

Two addresses in each subnet are reserved: one for the network and one for the broadcast. That’s why usable hosts are calculated as 2^n - 2, where n is the number of host bits.

Can this tool help with public and private IP ranges?

Yes. It identifies whether the entered IP is part of a private range (like 192.168.0.0/16) or is publicly routable.

Key Related Topics

  • Subnetting
  • IP address ranges
  • Network planning
  • IPv4 classes
  • Usable IP calculation