Tool Introduction

The CIDR Subnet Calculator is an online tool designed for network administrators, IT engineers, developers, and students. It helps users quickly parse IP addresses in CIDR (Classless Inter-Domain Routing) format and calculate detailed subnet information, including network address, broadcast address, subnet mask (dotted decimal and bit length), available host IP range, and total number of hosts. Whether you are performing network planning, troubleshooting, or learning network knowledge, this tool provides accurate and efficient calculation services, greatly simplifying IP address management.

What is CIDR?

CIDR (Classless Inter-Domain Routing) is a set of standards used on the internet to more efficiently allocate IP addresses and route IP data packets. Before CIDR, IP addresses were divided into three classes: A, B, and C. This classful addressing method led to severe waste of IP address resources. CIDR solves this problem by introducing Variable Length Subnet Masks (VLSM), allowing network administrators to divide and allocate IP address blocks more flexibly according to actual needs. A CIDR address is usually expressed in the form of “IP address/prefix length”, for example, 192.168.1.0/24, where /24 indicates that the subnet mask has 24 '1' bits.

How to Use

Access the Tool: Open the CIDR Subnet Calculator page.
Enter Parameters: In the provided input box, paste or manually enter the CIDR format IP address you need to calculate. For example: 192.168.10.50/27.
Trigger Calculation: Click the “Calculate” or “Submit” button.
View Results: The calculation results will immediately be displayed at the bottom of the page in a clear list or table format.

Input Parameter Format:

IP Address: Must be a valid IPv4 address (e.g., 192.168.1.1).
Prefix Length: Separated by a slash /, followed by an integer representing the number of bits in the subnet mask, typically ranging from 8 to 32 (e.g., /24).
Complete Example: 192.168.1.0/24 or 10.0.0.100/16.

Output Result Format:

The tool will display the following key information in an easy-to-understand list or table format:

IP Address: Your original input IP address.
CIDR Prefix: Your original input CIDR prefix.
Subnet Mask: Dotted decimal format (e.g., 255.255.255.0).
Network Address: The network identifier address of this subnet (e.g., 192.168.1.0).
Broadcast Address: The broadcast address of this subnet (e.g., 192.168.1.255).
Available Host Range: The range of IP addresses within this subnet that can be assigned to hosts (e.g., 192.168.1.1 - 192.168.1.254).
Total Hosts: The total number of IP addresses this subnet can accommodate (including network address and broadcast address).
Available Hosts: The actual number of host IP addresses that can be assigned to devices.

Usage Example

Suppose we need to calculate the detailed information for IP address 192.168.100.12 in a /27 subnet.

Example Input Data: 192.168.100.12/27

Expected Output Results:

Attribute	Value
Input IP Address	192.168.100.12
CIDR Prefix	/27
Subnet Mask	255.255.255.224
Network Address	192.168.100.0
Broadcast Address	192.168.100.31
Available Host Range	192.168.100.1 - 192.168.100.30
Total Hosts	32
Available Hosts	30

Specific Operation Demonstration: The user enters 192.168.100.12/27 into the input box, clicks the “Calculate” button, and the page will display the detailed subnet information above.

CIDR Subnet Calculation Formulas

Understanding the underlying calculation principles of CIDR helps to better use and understand subnetting. Here are some core calculation formulas:

Subnet Mask: Calculated based on the prefix length (N). For example, /24 means the first 24 bits are 1, and the last 8 bits are 0, i.e., 11111111.11111111.11111111.00000000, which converts to 255.255.255.0 in decimal.
Total Hosts: 2^(32 - N), where N is the prefix length. This includes the network address and broadcast address.
Available Hosts: 2^(32 - N) - 2. Subtracting 2 is because the network address and broadcast address cannot be assigned to hosts.
Network Address: Obtained by performing a bitwise “AND” operation between the IP address and the subnet mask.
Broadcast Address: Obtained by setting all remaining host bits of the IP address's network portion (i.e., the result after ANDing with the subnet mask) to 1, or by performing a bitwise “OR” operation between the network address and the complement of the subnet mask.

Frequently Asked Questions

Q: What IP address types are supported? A: Currently, this tool primarily supports CIDR subnet calculation for IPv4 addresses.
Q: What is the format of the output results? A: The output results are displayed in a clear list or table format, containing key network information such as network address, broadcast address, subnet mask, available host range, and total number of hosts.
Q: What is the available host range? A: The available host range refers to the segment of IP addresses within a subnet that can be assigned to end devices (such as computers, servers, router interfaces, etc.), excluding the network address and broadcast address.
Q: Are there any usage restrictions? A: The main restriction is that the input format must strictly follow the IPv4 CIDR notation (e.g., 192.168.1.0/24), and the prefix length must be between 8 and 32. This tool does not handle IPv6 addresses or private IP address conversions.

Notes

Input Format: Please ensure that the input IP address and prefix length are in the correct format, e.g., 192.168.1.0/24. Any format error may lead to calculation failure or inaccurate results.
IP Address Validity: The input IP address should be a valid IPv4 address. Although the tool will try its best to parse, an invalid IP may lead to unexpected results.
Prefix Length Range: For IPv4, the prefix length should be an integer between 8 and 32. Values outside this range will lead to errors or calculation results that do not conform to actual network scenarios.
Result Interpretation: Carefully check the calculation results and understand the meaning of each field to ensure they meet your network planning needs. Especially the network address, broadcast address, and available host range, as they are critical information for network configuration.
Network Planning: This tool provides calculation assistance, but actual network planning and deployment still require comprehensive consideration of specific network topology, equipment, and security policies.