[2026] How to Add Unallocated Space to C Drive in Windows 11/10

Before You Start: Check the Disk Layout

Press Windows + X and select Disk Management. Once you identify your disk layout, match it with the table below to choose the most suitable method.

Note: The partition bars illustrate the position of each partition. Their lengths do not represent the actual disk capacity.

Free space inside D is not unallocated space. Shrinking D with Disk Management normally releases space after D, so D still blocks C.

How to Add Unallocated Space to C Drive?

Method 1: Add Adjacent or Nonadjacent Space with 4DDiG Partition Manager

Choose this option whenever the unallocated space is not right next to C:, sits on the left side, or is separated by Recovery or other partitions. It is also a safe route after a disk clone. The tool can move partitions and merge unallocated partition blocks in one operation while protecting your data.

4DDiG Partition Manager is the most flexible option. It can let you drag the boundary of C: across any free space on the same disk. No command-line knowledge is required.

• Download and install 4DDiG Partition Manager from the official site. Launch the program

  FREE DOWNLOAD

  Secure Download

  BUY NOW
• Select Partition Management and select the disk that contains your C drive and the unallocated space. Click the C: partition and choose the Resize/Move option.

• Drag the right boundary of C: to absorb the free space, or enter the exact size you want.

  

• Preview the new layout, then click Apply / Execute. Confirm the pending operations and wait for the process to finish. A reboot may be required.

  

• After the operation completes, open File Explorer or Disk Management to verify that the unallocated space has been added to C drive.

  

Method 2: Add Unallocated Space to C Drive with Disk Management

Use Disk Management only when the unallocated space is immediately adjacent to the right of the C drive. Windows cannot move partitions, so any intervening volume will keep the Extend Volume button grayed out.

• Press Win + X and select Disk Management.

• Locate the C: volume. Confirm that a black “Unallocated” block sits directly to its right. Right-click the C: partition and choose Extend Volume.

  

• In the Extend Volume Wizard, click Next. The available unallocated space should appear automatically.

• Accept the maximum size (or enter a smaller amount) and click Next, then Finish.

• Windows will expand C: instantly. No reboot is usually required. This is the fastest way to extend c drive when the layout allows it.

Notes

If Extend Volume is greyed out, do not immediately delete D, Recovery, EFI, or OEM partitions. The layout must be adjusted first.

Method 3: Extend C Drive with Unallocated Space Using DiskPart

DiskPart is useful for advanced users or when you prefer a command-line approach. Like Disk Management, it only works if the unallocated space is contiguous and to the right of C:.

• Search for Command Prompt, right-click it, and select Run as administrator. Enter:

  $diskpart

  $list volume

• Identify the volume number assigned to C, then enter:

  $select volume <number>

  Do not copy a fixed number from an example; verify the drive letter and capacity.

• To use all adjacent space, enter:

  $extend

• To add approximately 10 GB, enter:

  $extend size=10240

  The size value is measured in megabytes.

• After that, enter:

  $exit

  Verify the result in File Explorer.

Notes

If DiskPart reports that there is not enough usable free space, the space is probably nonadjacent, on another disk, or blocked by the current layout. Use Method 1.

Special Cases

After cloning to a larger SSD, extra capacity may appear behind a Recovery or OEM partition. Use Method 1, and keep the original disk unchanged until the new SSD boots successfully.

If the unallocated space is on another physical disk, it cannot normally be added to a basic C volume. Move large files to that disk, migrate Windows to a larger SSD, or replace the system drive instead.

FAQs About How to Add Unallocated Space to C Drive

Why is Extend Volume greyed out when unallocated space exists?

The space is usually not directly to the right of C, another partition blocks it, or it is on a different disk.

Why did shrinking D not help?

Disk Management shrinks D from its end, creating unallocated space after D. D therefore remains between C and the released space.

Does extending C erase files?

It normally preserves files, but back up important data and avoid interrupting the operation.

Conclusion

The correct method depends on the layout. Use Disk Management or DiskPart when unallocated space is directly to the right of C. Use 4DDiG Partition Manager when D, Recovery, or another partition blocks it, when the space is on the left, or when you need to transfer capacity from D. Always check the physical disk, back up files, save the BitLocker recovery key, and verify the result after Windows restarts.