Windows Exact Disk Partition Calculator
Helping you create exact partitions for Windows Disk Management. Calculate precise MB values for extending or shrinking volumes with perfect accuracy.
Extend Volume Calculator
Use this tool to calculate the exact amount of space in MB needed to extend your Windows volume:
- If you want to just convert GB to MB for Windows partition perspective, enter the value in "Desired new size (GB)" to get the exact value in MB.
- If you want to extend your existing drive from non-exact to exact partition, enter the Desired new size (GB) and Current visible volume size (GB)to get a precise value to use in Disk Management.
How to use Extend Volume Calculator:
Step 1: Select your File System (NTFS is the default for modern Windows drives).
Step 2: Choose your goal below and enter the values accordingly:
Use this if you just want the exact MB value for a specific GB size.
- Leave "Current visible volume size" empty.
- Enter the amount in "Desired new size (GB)".
- The tool calculates the exact MB to input.
Use this to fix a partition size (e.g., change 137GB to exactly 150GB).
- Enter the "Current visible volume size" (e.g., 137).
- Enter the "Desired new size" you want to end up with (e.g., 150).
- The tool calculates the exact difference to extend.
Step 3: (Optional) Enter the "Maximum available space" from Disk Management to verify you have enough unallocated space.
Step 4: Click Calculate, then click Copy and paste the value into Windows Disk Management.
Shrink Volume Calculator
Use this tool to calculate exactly how much space in MB you can shrink from an existing Windows drive. Enter the Desired new size (GB), Total size before shrink (MB) and Available shrink space (MB) to get a precise value to use in Disk Management for resizing your current partition safely.
How to use Shrink Volume Calculator:
Step 1: Select your File System (NTFS is the default for modern Windows drives).
Step 2: Enter the Desired new size in GB. This is the final size you want your volume to have after shrinking.
Step 3: Locate the following values in Windows Disk Management (Right-click drive > Shrink):
• Total size before shrink (MB): The full current capacity of your volume.
• Available shrink space (MB): The maximum space Windows reports you can actually remove.
Step 4: Enter those values into the calculator and click Calculate.
Step 5: Copy the resulting MB value and paste it into the "Space to shrink in MB" field in Windows Disk Management.
About SwitchFirewall
SwitchFirewall is a technology-focused platform that provides accurate, practical tools for system administrators, IT professionals, and Windows users who require precise and reliable calculations.
Storage vendors calculate disk size using decimal units, while Windows displays and manages disk space using binary-based calculations. This difference often causes newly created or resized partitions to appear smaller than the expected size.
This calculator bridges that gap by generating the correct Windows-compatible MB value. Using the provided number ensures that the partition created during shrink or extend operations reflects the intended size accurately and appears correct within Windows Disk Management.
All calculations are performed locally in your browser. No data is transmitted, stored, or processed on any server, ensuring complete user privacy.
SwitchFirewall focuses on building transparent, purpose-driven utilities that solve real-world system administration challenges with accuracy and consistency.
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Precise Calculations
Get exact MB values for Windows Disk Management operations. No more guesswork or trial-and-error with partition sizes.
File System Support
Works with both NTFS and FAT32 file systems. Automatically adjusts calculations based on your selected file system type.
Visual Representation
See a visual representation of your disk partitions before and after operations. Understand exactly how your space will be allocated.
Safe & Secure
All calculations happen in your browser. No data is sent to any server, ensuring your privacy and security.
Free to Use
No registration, no hidden costs. This tool is completely free for personal and commercial use.
Time-Saving
Save time with instant calculations and one-click copy functionality. No more manual conversions or repeated attempts.
❓ Frequently Asked Questions
This tool calculates the exact MB values required by Windows Disk Management when extending or shrinking a partition. It helps you achieve precise disk sizes without guesswork or trial-and-error.
Windows performs partition operations internally using megabytes (MB) for better precision. Although sizes are displayed in GB, the resize operation requires MB input. This calculator converts GB to Windows-accurate MB values.
Disk manufacturers use decimal units (1 GB = 1000 MB), while Windows uses binary units (1 GB ≈ 1024 MB). This difference makes disks appear smaller in Windows, but no space is missing or lost.
This tool uses Windows Disk Management–aligned calculations, not vendor marketing values. This ensures the final partition size in Windows matches exactly what you requested.
Minor differences can occur due to file system overhead, Windows rounding rules, and reserved system space. These variations are normal and do not affect disk functionality.
Yes. The calculator supports both NTFS and FAT32 and adjusts calculations accordingly. Note that Windows limits FAT32 partitions to a maximum size of 32GB.
Yes. This calculator works with internal drives, external HDDs, SSDs, USB flash drives, and portable SSDs — as long as the volume is managed through Windows Disk Management.
Yes. The tool runs entirely in your browser, does not access your disk, and sends no data to any server. Always back up important data before resizing partitions.
🔐 Privacy Policy
Your privacy is important to us. This website is designed to provide simple disk and partition calculation tools with minimal data handling.
Data Collection
We do not collect, store, or transmit personal information such as names, email addresses, IP addresses, disk identifiers, MAC addresses, or device details.
All calculations performed by our tools run locally within your browser. Input values are not sent to our servers or stored in any database.
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Policy Updates
This privacy policy may be updated periodically to reflect changes in tools, advertising, or legal requirements. Updates will be posted on this page.
⚠️ Disclaimer
The tools and calculators provided on this website are for informational and educational purposes only.
While we aim for accuracy, calculated values may vary due to file system overhead, reserved space, rounding differences, or operating system behavior.
No Guarantee of Results
Disk size and partition calculations are based on commonly used industry and Windows standards. Actual results may differ depending on system configuration.
User Responsibility
You are solely responsible for any disk operations performed using values obtained from this website. Always back up important data before modifying disk partitions.
No Liability
We shall not be held liable for data loss, system failure, hardware damage, or any other issues arising from the use of these tools. Use them at your own risk.
Not Professional Advice
This website does not provide professional IT, data recovery, or hardware repair advice. For critical systems or enterprise environments, consult a qualified professional before making disk changes.