Add Unallocated to C

Merge/Add Unallocated space to C drive volume

This article introduces how to add Unallocated space to C drive on Windows 10/8/7/Vista/XP and Server 2019/2016/2012/2008/2003 without losing data.

About Unallocated space

As its name, Unallocated space is part of disk space that is not allocated to any partition. However, it doesn’t mean it’s blank. If there are files once saved to this area, they still can be recovered by some tools. To save new files to this area, you must create new volume with this Unallocated space and format with a file system.

In Disk Management of Windows Server 2008 and subsequent versions, or with disk partition software, you can also add Unallocated space to C drive or other volumes. Then Unallocated will be converted to part of free space.

How to get Unallocated space

There are two ways by deleting or shrinking an allocated partition.

After deleting a volume, all disk space of it will be converted to Unallocated. (Tips In MBR style hard disk, if you delete a Logical partition, disk space will be shown as Free instead of Unallocated.)

If you shrink a volume, part of free unused space will be converted to Unallocated. By this way, you won’t lose files in this volume, so it’s better.

How to add unallocated space to C drive

System partition C running out of space is very common in all Windows versions. To fix the low disk space issue without reinstalling Operating System and programs, many people want to move free space from D to C drive. Before extending C drive, you must get Unallocated space by deleting or shrinking other partition.

Windows native Disk Management can help you get Unallocated space easily, but it is not the best tool to add Unallocated space into C drive, because:

  • Extend Volume can only add Unallocated space to the drive that is adjacent and on its left side.
  • Unallocated space shrank from drive D is nonadjacent to C, if you right click C drive, Extend Volume is grayed out.

Extend Volume greyed out

To add Unallocated space into C drive, you must move it to the left side with partition software.

Steps to move and add Unallocated space to C drive:

Step 1: Download NIUBI Partition Editor, right click drive D and select “Resize/Move Volume“.


In the pop-up window, drag the middle position towards the right side.

Move D

Click OK, NIUBI moved Unallocated space next to C drive (from right of D to the left side).

Unallocated moved

Step 2 Right click C drive and select “Resize/Move Volume” again, drag the right border rightwards in the pop-up window.

Extend C

NIUBI added Unallocated space to C drive and the size is increased to 50GB.

System drive extended

Tip This software is designed to work in virtual mode, the 2 operations are listed as pending on bottom left as you see. To modify real disk partition, you need to click Apply to take effect.

In fact, NIUBI can shrink partition D and generate Unallocated space on its left side, so you can add Unallocated space to system C drive without moving. To do this, right click D and select “Resize/Move Volume”, and then drag the left border rightwards in the pop-up window.

Shrink D

Better than other disk partition tools, NIUBI Partition Editor provides unique 1 Second Rollback, Virtual Mode and Cancel-at-will technologies to ensure system and data intact. Furthermore, it is much faster because of its special file-moving algorithm.

In Summary

Windows native Disk Management utility helps you shrink a volume easily but it can’t add Unallocated space to C drive, because it cannot produce or move Unallocated space on the left side. 3rd party software is needed to accomplish this task, however, remember to back up and use the safe tool.

Drag the middle position in the pop-up window, you can add nonadjacent Unallocated space to C drive, drag the border towards other side, you can merge contiguous Unallocated space.