How to Add Unallocated Space to C Drive Without Losing Data

By James, Updated on: November 10, 2021

Unallocated space is part of disk space that is not belong to any partition. Besides creating new partition, you can add Unallocated space to C: drive or other volume to increase free space. To add Unallocated space to a partition, Windows native Disk Management is an option, but it can only add Unallocated space to the left contiguous partition. If you want to add to the right contiguous or any nonadjacent partition, you need 3rd-paty partition software. In this article, I'll introduce how to add Unallocated space to C drive in Windows Server and PC.

Applies to: Windows 11, Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, Windows Server 2022, Windows Server 2019, Windows Server 2016, Windows Server 2012 (R2), Small Business Server 2011, Windows Server 2008 (R2) and Windows Server 2003 (R2).

1. How to add Unallocated space to C drive after deleting D

To get Unallocated space you may either delete or shrink a volume. If you've gotten Unallocated space by deleting the contiguous partition D, you can merge Unallocated space without any software. Note: this method is invalid for Windows XP and Server 2003, because there's no Extend Volume function in Disk Management.

Steps to add Unallocated space to C drive with Windows Disk Management:

  1. Press Windows and R together on the keyboard, input diskmgmt.msc and press Enter to open Windows Disk Management.
  2. Right click C: drive and select Extend Volume.
  3. Simply click Next till Finish in the pop-up Extend Volume Wizard.

If D: is Logical drive, its disk space will be converted to Free instead of Unallocated after deleting. In that case, Disk Management is unable to extend C drive. When you right click C drive, Extend Volume is grayed out. If you encountered this issue, you may use another native tool - diskpart command.

How to add Unallocated space to C drive using diskpart cmd:

  1. Press Windows and R keys together, input diskpart and press Enter.
  2. Input list volume and press Enter in the command window, then you'll see all single partitions in a list. (Unlike Disk Management, Unallocated space is not listed).
  3. Input select volume C and press Enter.
  4. Input extend and press Enter, done.

2. How to add Unallocated space to C drive after shrinking D/E

If you got Unallocated space by shrinking D or other partition, You cannot add Unallocated space to C drive with Windows Disk Management or diskpart command. Because the built-in Extend Volume function can only merge Unallocated space to the left contiguous partition. Unallocated space that shrunk from D drive is nonadjacent to C, so Extend Volume is disabled. In this case, you need to move Unallocated space next to C drive in advance.

Steps to add Unallocated space to C drive after shrinking D:

  1. Download NIUBI Partition Editor, right click D: drive and select "Resize/Move Volume", drag the middle of D drive towards right in the pop-up window. Then Unallocated space is moved from right side of D to the left.
  2. Right click C: drive and select "Resize/Move Volume" again, drag right border towards right in the pop-up window, then Unallocated space is added into C drive.
  3. Click Apply on top left to execute. (All operations before this step only works in virtual mode.)

Video guide

If the right contiguous partition is E: in your computer, simply replace D with E in the steps above.

3. Add Unallocated space to system C drive with another disk

In some computer, the system partition is almost full but there's large amount of free space on another disk. Some people are wondering if it's possible to add Unallocated space to C drive from another disk.

In fact, neither Windows Disk Management nor 3rd-party software can do this. Because the size of a physical disk is fixed. A 500GB disk can't be decreased to 400GB or increased to 600GB.

In this situation, you need to copy disk to larger one. Additional disk space will be shown as Unallocated at the end of disk. Follow the steps in the video to add more space to C drive with another disk.

Video guide

In Summary

Windows native Disk Management and diskpart command can only add Unallocated space to the left contiguous partition, so it is useless in most cases. 3rd party software is better choice to accomplish this task, however, remember to back up first and run safe partition editor tool.

Better than other software, NIUBI Partition Editor has unique 1-Second Rollback, Cancel-at-well and Virtual Mode technologies to protect your system and data. In addition, it is much faster because of its advanced file-moving algorithm, saving much time while moving partition with large amount of files in it. Besides moving and adding Unallocated space to C drive in Windows server and PC, NIUBI helps do many other operations.

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