Can't shrink C drive partition in Windows 10

Updated on: May 17, 2019

Sometimes you need to shrink C drive, for example: you forget to edit and create partition when installing Windows 10, so C drive occupy all disk space. In that case, you can create more volumes by shrinking C drive to release free space. If drive D is running out of space, you can also shrink C to extend it.

To shrink C drive, Windows 10 has Shrink Volume in native Disk Management utility, but many people feedback that they can't shrink C drive. In this article, I'll explain why unable to shrink C drive in Windows 10 Disk Management and easy method to solve this problem.

Why cannot shrink partition C: in Windows 10 DM

There are 2 common reasons why cannot shrink C: drive in Windows 10 Disk Management: inconsistent available space and unmovable files. I'll explain one by one.

1. Inconsistent available space

Actually, it is very easy to shrink system partition and data drives with Disk Management, simply right click this partition to select Shrink Volume functionality and then encounter the amount of space to shrink.

When shrinking a partition with Shrink Volume, Disk Management will calculate the used and available disk space to shrink, the default amount is maximum available space. In my computer, the available amount of space is 150264MB.

Enter amount

As we know, many types of files are writing into C drive continuously, so the available space maybe less than 150264MB when clicking Shrink. That means, you can't shrink C drive with default maximum space. I did this and I received the error message "There is not enough space available on the disk(s) to complete this operation."

Error message

In this situation, do not use the default maximum space, enter smaller amount to try.

2. Unmovable files

It is easy to fix the issue by reason 1, but if you encounter the second issue, you need professional disk partition software.

In my another test computer, I shrank C drive to smaller size without issue, but when I do it again, Disk Management shows 0 and Shrink button is greyed out. As you see, there is still 7.53GB free space in C: drive, but Disk Management doesn't allow to shrink it.

Can't shrink C

Have you noticed the tip in the middle: You cannot shrink a volume beyond the point where any unmovable files are located.

What does it mean?

For example, C drive is made up of 4 blocks. If the unmovable files are located in block 3, you cannot shrink C drive to block 2 or 1, although there is free space there. The unmovable files include Paging file, Hibernation and other large files.

Shrink C drive

What to do when can't shrink C drive in DM

As I said above, you need professional partitioning software in this situation. The files that are unmovable to Disk Management can be moved with NIUBI Partition Editor. In addition, Windows DM can only shrink C drive to left side and generate Unallocated on right side, but NIUBI can shrink C drive to either side.

Download NIUBI Partition Editor, you'll see all disk partition info on the right and available operations on the left.

Main window

Right click C drive and select "Resize/Move Volume", you have two options in the pop-up window:

1. Drag left border towards right

Resize partition C

Then you can shrink partition C towards right and make Unallocated space on the left side.

Shrink C

2. Drag right border towards left

Resize partition C

Then you can shrink partition C towards left and make Unallocated space on the right side.

Shrink C

Follow the steps if you want to shrink C to expand system reserved partition, or shrink C to expand D drive.

Besides shrinking and extending partitions, NIUBI Partition Editor helps move, merge, copy, convert, defrag, hide, wipe, scan disk partition, etc.