About SubnetCalc

What Is This App?

SubnetCalc is a free, browser-based tool that calculates all the key values for any IPv4 subnet — network address, broadcast address, usable host range, subnet mask, wildcard mask, and related IPv6 mappings. It also walks you through every step of the calculation so you can learn how the math works, not just get an answer.

Who Is It For?

• Network engineers — quick reference when designing or troubleshooting subnets
• Students — the step-by-step breakdown makes it a study aid for networking courses (CompTIA Network+, CCNA, etc.)
• Anyone configuring a home or small office network — figure out how many devices your subnet can support

How to Use

• Type an IPv4 address into the input field (e.g. 192.168.10.50)
• Select a CIDR prefix from the dropdown (e.g. /25)
• Click Calculate to see all subnet details and the full calculation walkthrough
• Use Clear to reset and try another address

Pages

• Calculator — the main subnet calculation tool
• Data Flow — an animated visual of how each JavaScript function passes data to the next
• About — this page
• Calculator — the main subnet calculation tool
• Data Flow — an animated visual of how each JavaScript function passes data to the next
• FAQ — tabbed answers to common subnetting questions
• About — this page

Technical Notes

The app is a single-page application with no dependencies, no server, and no data collection. All calculations run locally in your browser using bitwise operations on 32-bit integers. Your IP addresses never leave your device.