How to Add Unallocated Space to C Drive in Windows 10

The C drive running out of space is a common issue on Windows 10 computers. When it happens, nobody likes to restart from scratch. It would be ideal if we could extend the C drive without losing programs and data. Similar to previous versions, Windows 10 has an "Extend Volume" function in the native Disk Management tool. Many people shrink the D drive with another "Shrink Volume" function and get some unallocated space. But this space cannot be extended to the C drive, because "Extend Volume" is grayed out. This article introduces how to add unallocated space to the C drive in Windows 10 without losing data. You can move and merge unallocated space into the C drive with a free tool.

How to Merge Unallocated Space in Windows 10 with Disk Management

In the Windows 10 Disk Management console, you can get unallocated space by deleting or shrinking a volume. By shrinking a partition, a portion of the free space will be converted to unallocated, and files in this partition will remain intact, so it is better than deleting it. However, there are 2 major limitations:

1. Disk Management is not 100% safe when shrinking partitions, especially when there are both primary and logical partitions on a disk.
2. Disk Management can only create unallocated space on the right when shrinking a partition.

When extending a partition with Disk Management, there are another 2 limitations:

1. The partition to be extended must be formatted with the NTFS file system; any other types of partitions are not supported.
2. There must be adjacent unallocated space on the right of this NTFS partition.

When shrinking the D drive in Disk Management with the "Shrink Volume" function, unallocated space is created on the right of D. Because this space is non-adjacent to the C drive, "Extend Volume" is grayed out. To add this unallocated space to the C drive without using third-party software, you must delete the D drive. When there is contiguous unallocated space, "Extend Volume" is enabled for the C drive.

Steps to merge unallocated space into the C drive in Windows 10 via Disk Management:

1. Right-click the D: drive and select Delete Volume.
2. Right-click the C: drive and select Extend Volume, then simply click Next to finish the Extend Volume Wizard.

Two points you should know before doing this:

1. Remember to back up or transfer all files in the D drive to another place before deleting it.
2. If D: is a Logical drive, the method above is invalid, because "Extend Volume" is disabled even after deleting the D drive.

If D is a Logical drive or you do not want to delete it, you must move the unallocated space to the left with third-party software. To accomplish this task, NIUBI Partition Editor offers a free edition to help you. It is free for all Windows 11/10/8/7/Vista/XP home computer users. It is able to shrink, move, extend, merge, clone, convert, wipe, defrag, optimize partitions, scan bad sectors, and much more.

How to Move Unallocated Space Next to C Drive (to the Left)

Download the free edition, and you will see all connected storage devices with graphical partition layout and other parameters.

Right-click drive D and select "Resize/Move Volume", then drag the middle of the D drive to the right in the pop-up window.

How to Add Unallocated Space to C Drive in Windows 10 Computer

Right-click the C: drive in NIUBI Partition Editor and select "Resize/Move Volume" again, then drag the right border to the right in the pop-up window.

Watch the video on how to move and merge unallocated space into the C drive in Windows 10/8/7:

In Summary

If you have shrunk the D drive, Disk Management cannot merge the non-adjacent unallocated space into the C drive in Windows 10. Run NIUBI Partition Editor to move the unallocated space to the left and then merge it into the C drive.

If you have shrunk the non-adjacent E drive with Disk Management, you need to move E and D to the right one by one until the unallocated space is behind the C drive.

If you have not shrunk any partition, you can create unallocated space on the left of the D drive directly with NIUBI Partition Editor; then you can extend the C drive without moving the partition and the unallocated space.

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