Free IP Subnet Calculator: CIDR, Subnet Masks & Network Planning

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Calculate subnet masks, CIDR notation, wildcard masks, and host ranges in seconds. Built for network engineers, system administrators, and anyone configuring IP networks.

From the field: I built this because I got tired of doing subnet maths in my head during planning sessions. Whether I am designing an Azure VNet or segmenting my homelab, having a quick calculator saves time and prevents mistakes that are painful to fix after deployment.

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
Class A, B, C
Support for all standard network classes
/8 to /30
Complete CIDR range coverage
Real-time
Instant calculations as you type

Quick Start Guide

  1. Select your network class (A, B, or C)
  2. Enter your IP address
  3. Choose your subnet mask or adjust the slider
  4. 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






/24

1

254

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.

First Octet Range
192 – 223
Hex IP Address
C0.A8.00.01
Wildcard Mask
0.0.0.255
Mask Bits
24
Subnet Bits
0
Host Address Range
192.168.0.1 – 192.168.0.254
Subnet ID
192.168.0.0
Broadcast Address
192.168.0.255
Subnet Bitmap
Network + Subnet bits |
Host bits

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?

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.

Keep Reading

Related Guides

If you found this useful, these guides continue the journey:

The RTM Essential Stack - Gear I Actually Use

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