CIDR Calculator - Calculate Network Subnet Information

Our CIDR Calculator is a powerful networking tool that calculates comprehensive network information from CIDR (Classless Inter-Domain Routing) notation. CIDR is a method for allocating IP addresses and routing Internet Protocol packets. This calculator helps network administrators, developers, and IT professionals understand subnet configurations, plan network layouts, and troubleshoot networking issues.

What is CIDR?

CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing IP packets. It replaced the older classful network addressing system and allows for more flexible allocation of IP addresses. CIDR notation combines an IP address with a prefix length, written as:

IP_Address/Prefix_Length

For example, 192.168.1.0/24 means the network uses the first 24 bits for the network portion and the remaining 8 bits for host addresses.

Key Features

Network Address: The base address of the network
Broadcast Address: The address used to broadcast to all hosts on the network
Subnet Mask: The mask that defines the network portion of the address
Wildcard Mask: The inverse of the subnet mask, used in ACLs
Host Count: Total number of possible host addresses
Usable Hosts: Number of assignable host addresses (excluding network and broadcast)
IP Range: The complete range of IP addresses in the network
Network Class: Classification of the network (A, B, C, or special)
Real-time Calculation: Instant results as you type
Sample Data: Quick access to example CIDR notation

How to Use the CIDR Calculator

Enter CIDR Notation: Type or paste a CIDR notation (e.g., 192.168.1.0/24) in the input field
Use Sample Data: Click "Sample" to load example CIDR notation
View Results: Network information appears automatically below
Review Details: Check all calculated network parameters

Understanding CIDR Notation

Prefix Length

The number after the slash (/) indicates how many bits are used for the network portion:

/8 - 8 bits for network, 24 bits for hosts (16,777,216 hosts)
/16 - 16 bits for network, 16 bits for hosts (65,536 hosts)
/24 - 24 bits for network, 8 bits for hosts (256 hosts)
/32 - All 32 bits for network (single host route)

Example: 192.168.1.0/24

Network Address: 192.168.1.0
Broadcast Address: 192.168.1.255
Subnet Mask: 255.255.255.0
Wildcard Mask: 0.0.0.255
Total Hosts: 256
Usable Hosts: 254
IP Range: 192.168.1.0 - 192.168.1.255
First Usable: 192.168.1.1
Last Usable: 192.168.1.254

Common CIDR Prefixes

Prefix	Subnet Mask	Hosts	Usable
/8	255.0.0.0	16,777,216	16,777,214
/16	255.255.0.0	65,536	65,534
/24	255.255.255.0	256	254
/25	255.255.255.128	128	126
/26	255.255.255.192	64	62
/27	255.255.255.224	32	30
/28	255.255.255.240	16	14
/30	255.255.255.252	4	2

Use Cases

Network Planning

Plan network subnets, determine how many hosts you can support, and allocate IP address ranges efficiently. Essential for network architects and administrators designing new networks.

Subnet Configuration

Configure routers, switches, and network devices with correct subnet masks, network addresses, and broadcast addresses. Critical for proper network operation.

Troubleshooting

Diagnose network connectivity issues by verifying subnet configurations, checking if IP addresses are within the correct range, and understanding network boundaries.

Security Configuration

Configure firewall rules, access control lists (ACLs), and security policies that require understanding of network ranges and subnet boundaries.

Cloud Infrastructure

Plan and configure VPCs (Virtual Private Clouds), subnets, and network security groups in cloud platforms like AWS, Azure, or Google Cloud.

Understanding Network Components

Network Address

The first address in a subnet, representing the network itself. This address cannot be assigned to a host and is used for routing purposes.

Broadcast Address

The last address in a subnet, used to send data to all hosts on the network simultaneously. This address also cannot be assigned to a host.

Subnet Mask

A 32-bit number that masks an IP address and divides it into network and host portions. It uses 1s for network bits and 0s for host bits.

Wildcard Mask

The inverse of the subnet mask, used in access control lists (ACLs) and routing protocols. It uses 0s for network bits and 1s for host bits.

Special Cases

/31 Networks (Point-to-Point)

Used for point-to-point links where only 2 addresses are needed. In /31 networks, there is no network or broadcast address, and both addresses are usable.

/32 Networks (Host Route)

Represents a single host route. All 32 bits are used for the network portion, leaving no host bits. Used for specific host routing.

Best Practices

Plan Ahead: Calculate subnet requirements before configuring networks
Reserve Addresses: Account for network and broadcast addresses when planning
Use Appropriate Prefix: Choose prefix length based on actual host requirements
Document Networks: Keep records of all subnet configurations
Verify Calculations: Double-check network information before deployment
Consider Growth: Plan for future expansion when allocating subnets

Frequently Asked Questions

What's the difference between total hosts and usable hosts? Total hosts include the network address and broadcast address. Usable hosts exclude these two addresses, representing the actual IP addresses you can assign to devices. For example, a /24 network has 256 total hosts but only 254 usable hosts.

Can I use the network or broadcast address for a host? No, the network address and broadcast address are reserved and cannot be assigned to hosts. The network address identifies the network itself, and the broadcast address is used for network-wide broadcasts.

What is a wildcard mask used for? Wildcard masks are used in access control lists (ACLs) and routing protocols like OSPF. They specify which bits in an IP address should be matched. A 0 bit means "match this bit" and a 1 bit means "ignore this bit".

How do I choose the right prefix length? Choose a prefix length that provides enough host addresses for your needs while minimizing wasted addresses. For example, if you need 50 hosts, use /26 (64 total, 62 usable) rather than /24 (256 total, 254 usable) to avoid wasting addresses.

What does "Class A/B/C" mean in the results? This refers to the traditional classful network classification. Class A uses /8, Class B uses /16, and Class C uses /24. CIDR allows for more flexible prefix lengths, but the class designation helps understand the network size.

Technical Details

The CIDR Calculator:

Validates CIDR notation format and IP address ranges
Calculates subnet mask using bitwise operations
Determines network address by applying subnet mask to IP
Calculates broadcast address using bitwise OR with inverted mask
Computes host count using 2^(32-prefix) formula
Handles special cases like /31 and /32 networks
Provides real-time calculation with immediate feedback
Processes all data locally in your browser for privacy and security

All calculations are performed entirely in your browser using JavaScript. Your network information never leaves your device, ensuring complete privacy and security.