Calculate subnet masks, CIDR notation, wildcard masks, and host ranges in seconds. Built for network engineers, system administrators, and anyone configuring IP networks.
What This Tool Does
- ▸ Instant Calculations: Enter any IP address and subnet mask to get complete network information
- ▸ CIDR Support: Works with CIDR notation (/24, /16, etc.) and traditional subnet masks
- ▸ Complete Results: Get network ID, broadcast address, usable host range, and subnet bitmap
- ▸ No Signup Required: Free to use, no registration, no ads
Quick Start Guide
- Select your network class (A, B, or C)
- Enter your IP address
- Choose your subnet mask or adjust the slider
- View instant results including usable host range, network ID, and broadcast address
Perfect for: Configuring routers, planning network infrastructure, studying for CCNA/Network+ certifications, troubleshooting IP conflicts, designing VLANs, setting up home labs, or any networking task that requires subnet calculations.
Subnet Calculator
Results
The IP Subnet Mask Calculator enables subnet network calculations using network class, IP address, subnet mask, subnet bits, mask bits, maximum required IP subnets and maximum required hosts per subnet.
Understanding IP Subnetting
Subnetting is the process of dividing a network into smaller, more manageable sub-networks (subnets). This improves network performance, enhances security, and makes IP address management more efficient.
Key Concepts
Subnet Mask
A 32-bit number that masks an IP address and divides it into network and host portions. Common masks include 255.255.255.0 (/24) for Class C networks.
CIDR Notation
Classless Inter-Domain Routing notation (e.g., /24) represents the number of bits used for the network portion. /24 means 24 bits for network, leaving 8 bits for hosts.
Network Address
The first address in a subnet, used to identify the network itself. All host bits are set to 0 (e.g., 192.168.1.0 for a /24 network).
Broadcast Address
The last address in a subnet, used to send data to all hosts on the network. All host bits are set to 1 (e.g., 192.168.1.255 for a /24 network).
Why Subnet?
- Improved Performance: Smaller broadcast domains reduce network congestion
- Enhanced Security: Isolate sensitive departments or services
- Efficient IP Management: Better utilize available IP address space
- Geographic Organization: Separate networks by location or function
How to Use a Subnet Calculator
A subnet calculator is an essential tool for network engineers that automates the complex binary mathematics involved in subnetting. Instead of manually converting IP addresses to binary and calculating subnet ranges, you can get instant, accurate results.
Common Use Cases
Network Planning
Determine how many subnets you can create and how many hosts each subnet can accommodate before deploying infrastructure.
Troubleshooting
Verify that devices are configured with correct IP addresses within their designated subnet ranges to resolve connectivity issues.
Exam Preparation
Practice subnetting problems for Cisco CCNA, CompTIA Network+, or other networking certifications. Check your work instantly.
Understanding the Results
- Network ID (Subnet ID)
- The first address in your subnet range, used to identify the network itself. Cannot be assigned to hosts.
- Broadcast Address
- The last address in your subnet, used to send messages to all devices on the network. Cannot be assigned to hosts.
- Usable Host Range
- The IP addresses between the network ID and broadcast address that can be assigned to devices.
- Wildcard Mask
- The inverse of the subnet mask, commonly used in Cisco ACLs (Access Control Lists) and OSPF configurations.
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation is a compact way to represent IP addresses and subnet masks. The number after the slash (/) indicates how many bits are used for the network portion. For example, /24 means 24 bits for the network, leaving 8 bits for hosts.
Why are two addresses unusable?
Every subnet reserves two addresses: the network ID (first address) identifies the network itself, and the broadcast address (last address) is used to communicate with all devices on the network. Neither can be assigned to individual hosts.
What’s the difference between Class A, B, and C?
Network classes are determined by the first octet: Class A (1-126) uses 8 bits for the network, Class B (128-191) uses 16 bits, and Class C (192-223) uses 24 bits. This determines the default subnet mask and how many hosts the network can support.