Cannot/unable to extend C drive in Windows 10

Updated on: May 17, 2019

This article explains why cannot extend C drive in Windows 10 Disk Management and what to do when you are unable to expand C drive.

Unable to extend C

Why cannot extend C drive in Windows 10 DM?

Microsoft adds new Shrink Volume and Extend Volume from Windows Vista Disk Management, which can be used to decrease and increase size of allocated partitions. However, both functions have restrictions. Windows 10 inherited these functions without any improvement, so you'll encounter many issue when you resizing hard drive partitions with this native utility.

Searching by Google and you'll find similar problem in technical forums: many people are unable to extend C: drive in Windows 10 Disk Management even by shrinking or deleting partition D.

Then what is the reason? In a word, there is no adjacent Unallocated space on the right side.

Before extending a volume, there must be Unallocated space. If you did not delete or shrink a partition to get Unallocated space, of course you cannot extend C drive.

When right clicking C drive, Extend Volume is grayed out.

No adjacent space

By deleting a partition, all files in it will be deleted, too. If there is no other partition to transfer files, or programs are installed in this partition, you cannot delete it.

Besides Extend Volume, there is Shrink Volume function in Windows 10 Disk Management, so many people want to get Unallocated space by shrinking partition.

But, they still cannot expand C drive after shrinking D. This is the most common situation that people feedback unable to extend C drive in Windows 10 Disk Management.

If you have tried to shrink D drive, you'll know that Shrink Volume only provide you an option to enter amount of space, and then Unallocated space will be made on the right side of D for you.

Extend Volume can't extend C: drive except that you move this Unallocated space next to C drive.

Unable to extend C

In fact, there are other reasons that could cause Extend Volume grayed out, for example:

Few people use FAT32 for system C drive, and Windows 10 use GPT disk by default, so few people will encounter such issue.

The solution when unable to extend C drive in Windows 10 DM

To solve this problem, it is very easy. You just need 1 step to move the Unallocated space behind C drive, and then Extend Volume will be enabled.

Download NIUBI Partition Editor and you'll see all disk partitions with structure and other information. There is 20GB Unallocated space that is shrinking from drive D.

NIUBI Partition Editor

To move Unallocated space:

Right click drive D and select "Resize/Move Volume", drag middle position rightwards in the pop-up window.

Move drive D

Then Unallocated space is moved from right side of D to the left.

Move Unallocated

To extend C drive:

Right click drive C and select "Resize/Move Volume, drag right border towards right in the pop-up window.

Extend C drive

Then Unallocated space is combined into system C drive.

Extend volume C

NIUBI is designed to work in virtual mode to avoid mistake, real disk partition won't be modified until click Apply on top left to confirm.

Watch the video how to move Unallocated space and extend C drive:

Video guide

In Summary

Although Windows 10 Disk Management has built-in Shrink and Extend Volume, it is useless if you want to extend a drive by shrinking other one. Unallocated space can only be made on the right side of D via Shrink Volume, Extend Volume is unable to extend C drive with this non-adjacent Unallocated space.

To solve this problem, simply move Unallocated space to behind C drive. If you have not shrank, partition D, you can make Unallocated space on the left side directly with NIUBI Partition Editor. Besides resizing and moving partition, it helps you merge, convert, copy, defrag, wipe, hide, scan partitions, etc.