How to Merge Unallocated Space into Your C: Drive (Using Command Prompt)

(Suggested Featured Image: A split image showing a nearly full C: drive on one side and a healthy, spacious one on the other.)

Is your C: drive flashing that dreaded red "Low Disk Space" warning? It’s a common headache, especially as applications and updates grow larger. While moving files can help, sometimes you need a more permanent solution.

 If you have a separate partition (like a D: drive) right next to your C: drive, you can actually merge them to give your system room to breathe. Today, we’re diving into the powerful Diskpart utility in the Command Prompt to do just that.

⚠️ A Critical Warning Before We Begin

This process involves deleting a partition. This will erase all data on it permanently.

• BACK UP EVERYTHING from the partition you plan to delete to an external hard drive or cloud storage.

• The unallocated space you create must be immediately to the right of your C: drive to be merged. The extend command cannot jump over other partitions.

(Image Suggestion: A simple diagram showing a C: drive, then an empty space (unallocated), then another partition. A red "X" over the second partition, indicating it can't be used if it's not contiguous.)

[Diagram: C: Drive | Unallocated Space | D: Drive] -> ✅ CAN BE EXTENDED
[Diagram: C: Drive | D: Drive | Unallocated Space] -> ❌ CANNOT BE EXTENDED

If you're backed up and ready, let's get started.

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Step-by-Step Guide: Merging Partitions with Diskpart

Step 1: Open Command Prompt as Administrator

We need elevated privileges to make these system-level changes.

1. Click the Start button or press the Windows key.

2. Type cmd.

3. Right-click on Command Prompt and select Run as administrator.

4. Click Yes when the User Account Control (UAC) prompt appears.

(Image Suggestion: A screenshot of the Windows Start menu with "cmd" typed, highlighting the "Run as administrator" option.)

https://i.imgur.com/example-admin-cmd.png

Step 2: Launch the Diskpart Utility

In the black Command Prompt window, type the following command and press Enter:

text

diskpart

A new prompt saying DISKPART> will appear. This is your signal that you're now inside the disk partitioning tool.

Step 3: Identify Your Disks and Partitions

We need to see the layout of your storage.

1. To list all the physical disks, type:

   text

   list disk

   You'll see a list like the one below. Identify the disk that contains your C: drive (usually Disk 0). Note its number.

   (Image Suggestion: A screenshot of the list disk command output, with an arrow pointing to "Disk 0".)

   https://i.imgur.com/example-list-disk.png

2. Select that disk (replace 0 with your disk number if different):

   text

   select disk 0

3. Now, list the partitions on that disk to see the current layout:

   text

   list partition

   This is the most important view. Identify your C: drive partition and the partition you wish to delete (e.g., D: drive). Note their partition numbers.

Step 4: Delete the Target Partition (This Erases Data!)

This is the point of no return. Double-check you've backed up the data!

1. Select the partition you want to delete (replace Y with its number):

   text

   select partition Y

2. Delete it. This command will immediately wipe the partition and turn it into unallocated space.

   text

   delete partition

   Tip: If you get an error, the partition might be in use. Try the command delete partition override.

Step 5: Extend Your C: Drive

Now for the rewarding part—adding that space to your C: drive.

1. First, select your C: drive volume:

   text

   select volume C

2. Finally, extend it into the now-available unallocated space:

   text

   extend

   The extend command will automatically use all contiguous unallocated space to the right.

Step 6: Exit and Confirm

You're all done! Exit the Diskpart utility and then close the Command Prompt window.

text

exit

Then type exit again to close the Command Prompt.

Open File Explorer, and you should see your C: drive looking much healthier with its newfound free space!