Cannot Extend C Drive Volume in Windows 10/8/7 - How to Fix

by John, Updated on: October 17, 2022

Nowadays, many Windows 10 computers use SSD for Operating System and programs. It is helpful to improve computer performance. But on the other hand, SSD is much smaller because it is still expensive. So C: drive is more likely running out of space. In Windows 7/8/10 Disk Management, there are "Shrink Volume" and "Extend Volume" functions to help resize partition without losing data. Many people successfully shrunk D (or E) drive but cannot extend C drive in Windows 10 Disk Management, because Extend Volume option is grayed out . In this article, I'll explain the reasons why you cannot extend volume in Windows 10/8/7 Disk Management, and what to do when you cannot extend C drive in Windows 10/8/7 computer.

Why you can't extend C drive in Windows 10/8/7 Disk Management

Reasons 1: no Unallocated space next to C drive

In a Windows computer, there are 3 types of space on a hard disk:

Besides creating new volume, Unallocated space can be used to extend other partition. Because the size of a physical disk is fixed, before extending a partition, you must delete or shrink another partition to get Unallocated space. Without such kind of space, of course you cannot extend volume in Windows 10/8/7 via Disk Management.

Obviously, it is better to get Unallocated space by shrinking partition, because you won't lose files in it. The problem is, you still can't extend C drive in Windows 10/8/7 even after shrinking D or any other partitions, because Disk Management has 2 major shortages:

  1. "Shrink Volume" function can only make Unallocated space on the right when shrinking a partition.
  2. "Extend Volume" function can only extend Unallocated space to the contiguous partition on the left.

As you see in the screenshot, I got 20GB Unallocated space on the right of D after shrinking this partition. This space is nonadjacent to C drive, so I cannot extend C: drive. This is the most common reason why you cannot extend C drive in Windows 10/8/7 with Disk Management tool.

Extend Volume greyed out

Reasons 2: the contiguous partition is Logical

Because Extend Volume is disabled for C drive after shrinking D, some people are wondering if it works by deleting D drive to get adjacent Unallocated space. To answer this question, I deleted the adjacent D drive in my test computer. As you see, Disk Management is still  unable to extend C drive in Windows 10.

After deleting D

After deleting E

Why is there such strange issue?

MBR GPT disk

In Windows computer, there are 2 types of disk - GPT and MBR. On GPT disk, all partitions are created as Primary. But on MBR disk, there could be Primary and Logical partition. In addition, you can only create maximum 4 Primary partitions, or 3 Primary partitions plus an Extended partition on MBR disk.

Primary partition works as an independent unit, but Logical partition is part of the Extended partition. After deleting a Primary partition, its disk space will be changed to Unallocated, but after deleting a Logical partition, it will be changed to Free space.

In Disk Management, Unallocated space can't be extended to any Logical partition. Free space can't be extended to any Primary partition. In a word, if you want to extend C drive by deleting D in Disk Management, D must be Primary partition, because C drive is always Primary. (Note: D drive in this article means the adjacent partition behind C drive.)

What to do when you cannot extend C drive in Windows 10/8/7

Follow corresponding solution according to your own disk partition configuration.

Method 1: move partition and Unallocated space

As I explained above, Disk Management can't extend C drive with nonadjacent Unallocated space. Therefore, you need to move Unallocated space from right side of D to the left.

Steps when you can't extend C drive in Windows 10/8/7 after shrinking D/E:

Step 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.

Move drive D

Then Unallocated space will be moved to the left side.

Move Unallocated

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

Extend C drive

Then C drive will be extended by merging this Unallocated space.

Extend volume C

This program is designed to work in virtual mode to avoid mistake, to modify real disk partition, you need to click Apply on top left to take effect.

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

Video guide

Method 2: shrink and extend partition with NIUBI

If the contiguous partition D is a Logical drive, as I explained above, Disk Management is unable to extend C drive by either shrinking or deleting D. But, it is very easy to solve this problem with NIUBI Partition Editor.

  1. Right click D drive and select "Resize/Move Volume", drag left border towards right in the pop-up window, then Unallocated space is made on the left.
  2. Follow step 2 above to add Unallocated space to C drive.

If you've deleted D drive, recreate it in Disk Management and follow the same steps above.

Other reasons why cannot extend volume in Windows 10/8/7

When you extend a data partition with Windows Disk Management, you may encounter additional issue.

  1. FAT32 partition can't be extended even if there's contiguous Unallocated space on the right. Because Disk Management can only extend NTFS partition.
  2. Disk Management cannot extend volume beyond 2TB on a MBR disk.

Additional methods when you cannot extend volume in Windows 10/8/7:

  1. To NIUBI Partition Editor, there's no difference if you use FAT32 or NTFS partition. If there's adjacent Unallocated space, simply combine with NIUBI.
  2. To extend a volume larger than 2TB, convert MBR disk to GPT in advance with NIUBI.
  3. If you want to extend the right partition E after shrinking D, you just need to run "Resize/Move Volume" for E drive and drag left border towards left in the pop-up window.

Drag to extend

When you can't extend volume in Windows 10/8/7, run NIUBI Partition Editor and follow corresponding method above. Besides help fix this issue easily, this tool helps you do many other disk partition management operations such as copy, convert, merge, defrag, wipe, hide partition, scan bad sectors, etc.