How to Calculate Subnets and CIDR Ranges Online
Network planning and IP address management require understanding subnets and CIDR notation. Whether you're configuring a home network, setting up VLANs, or managing cloud infrastructure, knowing how to calculate subnet masks, usable IP ranges, and broadcast addresses is essential. This guide shows you how to calculate subnets and CIDR ranges using fixie.tools — completely free, no signup required.
Step 1: Open the Subnet Calculator
Navigate to fixie.tools/subnet in your web browser. The tool works on all devices without requiring any account creation. All calculations happen instantly in your browser.
Step 2: Enter Your Network Information
Input either an IP address with CIDR notation (like 192.168.1.0/24) or enter the IP address and subnet mask separately. CIDR notation is more common in modern networking — the slash number indicates how many bits belong to the network prefix. For example, /24 means the first 24 bits (first three octets) are the network portion.
Step 3: View Network Details
Once you enter valid network information, the calculator instantly displays comprehensive subnet details. You'll see the network address (first IP in the range), broadcast address (last IP in the range), first usable host IP, last usable host IP, total number of hosts, wildcard mask (used in ACLs), and subnet mask in both decimal and binary notation. All calculations are performed in real-time as you type.
Step 4: Understand CIDR Notation
The calculator explains what your CIDR range means. For example, /24 gives you 256 total IPs with 254 usable hosts (network and broadcast addresses aren't usable). Common ranges include /24 (256 IPs, typical home/small office), /16 (65,536 IPs, large corporate networks), and /8 (16.7 million IPs, major ISPs). Smaller CIDR numbers mean larger networks.
Step 5: Plan Your Network Subnetting
Use the calculator to plan subnet division for your network. If you have a /24 network and need to divide it into smaller subnets, try /25 (128 IPs, 2 subnets), /26 (64 IPs, 4 subnets), or /27 (32 IPs, 8 subnets). The calculator helps you visualize how many devices each subnet can accommodate and how to allocate IP ranges efficiently.