DiskPart Extend C Drive with Unallocated Space

When the Windows C drive runs out of space, system performance drops and updates may fail. If unallocated space exists on your disk, you can use DiskPart to extend the C drive without reinstalling Windows.

Quick Answer: You can extend the C drive with DiskPart only if the unallocated space is directly next to the C drive right. If the space is not adjacent, DiskPart will fail and a free tool like IM-Magic Partition Resizer is required.

Links

• What is Diskpart
• How to Extend C Drive with DiskPart
• Common DiskPart Errors and Fixes
• Why DiskPart Cannot Extend the C Drive
• Diskpart Difficult or Fails? Try IM-Magic Partition Resizer

What Is DiskPart

DiskPart is a built-in Windows command-line utility used to manage disks, partitions, and volumes. It allows advanced users to extend volumes, including the system C drive.

Requirements Before Extending C Drive

• Unallocated space must be adjacent to the C drive
• The C drive must use the NTFS file system
• Administrator privileges are required
• No recovery partition between C drive and unallocated space

How to Check Unallocated Space Location

• Press Win + X → Select Disk Management
• Locate the C drive
• Check whether the unallocated space is directly after the C drive

If another partition (such as Recovery or OEM) is between them, DiskPart will not work.

How to Extend C Drive with DiskPart

Step 1: Open Command Prompt

Search for Command Prompt, right-click it, and select Run as administrator.

Step 2: Start DiskPart

Type diskpart and press Enter.

Step 3: Select Disk and Volume

Use the following commands carefully:

• list disk
• select disk 0
• list volume
• select volume C

Step 4: Extend the C Drive

To use all available unallocated space:

extend

To extend by a specific size (in MB):

extend size=10240

(Example: 10240 MB = 10 GB)

Step 4: Exit

Type exit to end the Diskpart.

Also read: Extend c drive using Diskpart

Common DiskPart Errors and Fixes

Error: “There is not enough usable free space”

Cause: Unallocated space is not adjacent to the C drive
Fix: Delete or move the partition between C drive and unallocated space

Error: “The volume cannot be extended”

Cause: File system is not NTFS or partition layout is unsupported
Fix: Convert FAT32 to NTFS or use a partition manager

Error: “DiskPart has encountered an error: Access is denied”

Cause: Command Prompt not run as administrator
Fix: Restart CMD with admin privileges

Why DiskPart Cannot Extend the C Drive

• Unallocated space is not contiguous
• A recovery, EFI or OEM partition blocks the extension
• The disk layout does not support resizing
• The C drive is not NTFS
• The unallocated space is not on the same disk
• Unallocated space is not at the right side of the C drive

Diskpart Difficult or Fails? Try IM-Magic Partition Resizer

IM-Magic Partition Resizer Free is a safe and user-friendly solution powered by Resize-C. It can extend the C drive even when unallocated space is not adjacent.

• Move partitions without data loss to change the location of the unallocated space
• Move recovery/EFI partitions
• Extend C drive without data loss
• No command-line usage required
• Supports Windows 11, Windows 10 to Windows XP for free, and a free domo for Windows Server

Video: How to create and move unallocated space to C drive with free tool IM-Magic Partition Resizer

Resize-C vs DiskPart Feature Comparison

Feature	DiskPart	Partition Resizer
Extend C Drive	Yes	Yes
Requires Adjacent Unallocated Space	Yes	YES
Move Partitions	No	Yes
2TB Max for MBR Disk	Yes	Yes
NTFS C Required	Yes	No
User Interface	Command-line	Graphical
Best for Beginners	No	Yes

Which Tool Should You Choose?

Choose DiskPart If

• The unallocated space is directly next to the C drive
• You are comfortable using command-line tools
• You want a built-in Windows solution

Choose Resize-C If

• DiskPart fails to extend the C drive
• Unallocated space is not contiguous
• A recovery partition blocks the C drive
• You want a safer and easier solution

Frequently Asked Questions

Is DiskPart safe to use?

DiskPart is safe when commands are used correctly, but mistakes can cause data loss. Backup is recommended.

Can I extend C drive without unallocated space?

No, DiskPart requires existing unallocated space to extend any volume.

What if DiskPart fails?

If DiskPart fails due to disk layout restrictions, Resize-C provides a reliable alternative.

Conclusion

Using DiskPart to extend the C drive with unallocated space is effective only under strict conditions. When those conditions are not met, Resize-C offers a flexible and safer way to resize the system partition without reinstalling Windows.