When the C drive (system partition) is out of space, the C drive is full, or you get a low disk space warning on Windows 10, and hardware upgrades become unavailable. Here is a real case from Microsoft Community:

I've tried disk management, but the extend option is grayed out. When I upgraded to Windows 10, it split the drives into C and D. The D had files that didn't belong to me, so I deleted them.

How to extend the C drive in Windows 10 could be bothering you for now. EaseUS will introduce how to extend partitions, especially to increase the volume of the C drive in Windows 10 successfully. 

Extend C drive

Method 1. Extend C Drive in Windows 10 With EaseUS Partition Manager Software

  • Difficulty Level: Easiest
  • Suitable for: Windows beginners and professionals

For users who want to extend the C drive with a professional and easy method, EaseUS Partition Master Professional is the right choice. As magic partition software, EaseUS Partition Master is a comprehensive hard disk partition management software that you can't miss. Also, this software works perfectly with hardware, even with RAID, and supports all Windows Operating Systems.

Free Download 

Windows 11/10/8/7100% Secure

Your data is completely protected during all operations. Let's see how to extend the volume of C drive in Windows 10 here:

Tutorial 1. Smart Extend C Drive with Low Disk Space Error

Step 1. Click "Adjust with 1-Click" to extend C drive.

When your C drive is out of space, hover your mouse over the C drive, you will see the Low Disk Space alert on EaseUS Partition Master. Click "Adjust with 1-Click" to extend it.

How to Adjust Low C Drive Space Step 1

Step 2. Click "OK" to extend C drive automatically.

By clicking "OK", EaseUS Partition Master will automatically allocate space to your C drive to solve the low space issue.

How to Adjust Low C Drive Space Step 2

Extra Option: You can also click "Manual Adjustment" to extend the C drive manually.

When turning to Manual Adjustment, select the C drive, and drag dots rightward to add more space to C drive. Click "OK" to confirm.

Manually Adjust Low C Drive Space

Step 3. Confirm to resolve low disk space in C drive

Click the "Execute Task" button at the top corner and start all pending operations by clicking "Apply".

How to Adjust Low C Drive Space Step 3

Do you see? This tool can help extend system partition in Windows 10 efficiently. Share this article to let more users know about this tool.


Tutorial 2. Extend C Drive With or Without Adjacent Unallocated Space

Option 1. Extend System C drive with unallocated space

  1. 1. Right-click on the System C: drive and select "Resize/Move".
  2. 2. Drag the system partition end into the unallocated space so to add it to the C: drive. And click "OK". 
  3. 3. Click "Execute Task" and "Apply" to execute the operations and extend the C drive.

Option 2. Extend System C drive without unallocated space

  1. 1. Right-click a big partition with enough free space on the system disk, select "Allocate Space".
  2. 2. Select the system drive at the Allocate Space From (*) To section, and drag the end of System C drive into the unallocated space. Click "OK" to confirm.
  3. 3. Click "Execute Task", it will list the pending operations, and click "Apply" to save the changes and extend the C drive.

0:00-0:26 Extend System Drive with Unallocated Space; 0:27-0:58 Extend System Drive without Unallocated Space.

  1. The program may pop up a window to ask you to restart your computer after executing the operation and do as the software requires.
  2. Your computer will restart with a bigger system C drive and better computer performance on your Windows 11/10 PC.

If you are experiencing a similar issue on Windows 11, Windows 8, or Windows 7, don't worry. Refer to the respective tutorial guide below to increase local disk C successfully on your PC:

Bonus Tip: Extend C Drive with Another Hard Drive/SSD

If you only have 1 system C drive on the disk, and it's full now, but you get a second drive with huge free space, relax. You can apply EaseUS Partition Master with its Extend with 2nd Disk feature for help. You may follow this guide for help:

related articles

How do you extend C Drive with another disk?

How to expand the C drive from another HDD or SSD? Follow the full guide below, and you'll successfully get rid of the SSD C drive full issue with ease.

Extend C drive with another disk

Aside from assisting you in extending system partition, this software lets you enjoy all the powerful functions, such as:

Free Download 

Windows 11/10/8/7100% Secure

Method 2. Extend C Drive in Windows 10 via Disk Management

  • Difficulty Level: Medium
  • Suitable for: Windows-experienced users

There must be unallocated space behind the partition you want to expand with Window's built-in Disk Management utility. Otherwise, you might find that the Extend Volume is greyed out and unavailable.

Asum that you have contiguous unallocated space next to the C drive, here is how to extend the C drive in Windows 10 using Disk Management:

Step 1. Press the Windows + R keys simultaneously to open the Run dialog.

Step 2. Type diskmgmt.msc and hit Enter to open the Disk Management utility.

You can also right-click This PC and choose "Manage -> Storage -> Disk Management".

Step 3. Right-click on the C drive and choose "Extend Volume".

extend windows 10 partition

Step 4. Set and add more size to the C drive and click "Next" to continue. 

Step 5. Click "Finish" to complete the process.

Extend Windows 10 partition with Disk Managenent

Note that if the unallocated space is not behind the C drive, you can revert to Method 1 and apply EaseUS Partition Master for help. 

🚩Read Also: How to Fix Cannot Extend Volume

Free Download 

Windows 11/10/8/7100% Secure

Method 3. Extend Volume of C Drive in Windows 10 via CMD

  • Difficulty Level: Medium
  • Suitable for: Windows experienced users and professionals

There is another tool named Diskpart, which also enables you to manage your local disk and partition. The Windows Command Prompt utility works the same as the Disk Management tool. One important point is that inexperienced users should not rush to this method because a tiny mistake can damage the entire hard drive. To do so, you'll also need to create unallocated space next to the C drive, then follow these steps below to extend the volume of the C drive using CMD:

Step 1. Press the Windows + X keys and choose "Command Prompt (Admin)".

Step 2. Type the following commands, and each one ends with the "Enter" key:

list volume
select volume x (x is the C drive number)
extend size =number (the number is the MB size for extending the C drive)

Extend C drive usign cmd

If there is no unallocated space, you can't extend the C drive in Windows 11/10 with this method. Follow and learn how to fix this issue:

related articles

Can't Extend C Drive in Windows 11? Here Is Why and How-to Fix

When you can't extend C drive in Windows 11 or older systems, relax and follow the fixes on this page for help.

Image of C drive

Bonus Tip: Upgrade Windows 10 OS Disk to a Larger Hard Drive, No Data Loss

Clone and replacing the old drive with a bigger one can also solve your problem. To do so, you have two options:

#1. Migrate Windows 10 to a New HDD/SSD without OS Reinstallation

If you don't want to migrate other data on the C drive, you can only migrate the Windows operating system to a new drive with the help of EaseUS Partition Master. 

Free Download 

Windows 11/10/8/7100% Secure

Video Tutorial: How to Migrate OS from HDD to SSD

#2. Upgrade Windows 10 OS Disk to a Bigger HDD/SSD

If you want to replace the whole C drive, both the system and the data, clone this drive with the help of EaseUS Partition Master. This feature lets you move your system and data to SSD/HDD easily and quickly. Follow the steps below to clone your drive:

Step 1. Select the source disk.

  • Click the "Clone" from the left menu. Select the "Clone OS Disk" or "Clone Data Disk"  and click "Next".
  • Choose the source disk and click "Next".

Step 2. Select the target disk.

  • Choose the wanted HDD/SSD as your destination and click "Next" to continue.
  • Read Warning message and confirm "Yes" button.

Step 3. View the disk layout and edit the target disk partition size. 

Then click "Continue" when the program warns it will wipe out all data on the target disk. (If you have valuable data on the target disk, back up it in advance.)

You can select "Autofit the disk", "Clone as the source" or "Edit disk layout" to customize your disk layout. (Select the last one if you want to leave more space for C drive.)

Step 4. Click "Start" to start the disk cloning process.

Also Read: How to Partition A Hard Drive in Windows 11/10

Other Tips to Extend the Volume of C Drive in Windows 10

In addition to these solutions, you may ask about a way to extend the volume of the C drive in Windows 10 with or without software. Here, you can learn other tips to reduce the possibility of a full C drive and resize the C drive.

  • Separate OS and personal data: move personal data to a non-system partition.
  • Merge partition to C drive: merge used or empty partition to C drive.
  • Run Disk Cleanup: clean up junk and temporary files to free up space in the C drive.
  • Empty recycle bin: The recycle bin content takes up C drive space, and when you empty the recycle bin, you can increase the disk space a bit.
  • Move the program to another drive: Transfer programs from the C to the D drive or other partitions also help free up space on the C drive.


In this article, we discussed how to extend the C drive in three reliable ways. After that, we also provided a bonus tip and practical tips to help users increase the volume of the C drive in Windows 10. If you want to resize your system partition, download EaseUS Partition Master and follow the mentioned methods.

Free Download 

Windows 11/10/8/7100% Secure

Related FAQ on How to Extend C Drive in Windows 10

In addition to extending the C drive, some people have asked related questions. Here are some examples:

1. Can we extend the C drive?

Yes, you can. You can use the third-party software, Disk Managemen or Diskpart to expand your C drive in Windows 11/10 easily. Among them, EaseUS partition software is my recommendation. It can extend any drive easily and quickly.

2. Can I extend C drive from D?

Yes, sure. You can extend the C drive from the D drive using unused free space. Here is how to do so:

  • Open Disk Management, right-click on D drive, and select "Shrink Volume."
  • Set the size of unallocated space you want to shrink from D drive and click "Shrink."
  • Click "OK".
  • Right-click on C drive and select "Extend Volume".
  • Select to add the created unallocated space to D drive, and click "OK."

3. Why extend the volume grayed out windows 11/10/8.1/7?

When you are using Disk Management to increase C drive space, you can right-click "Computer" and choose "Manage" to go, then you can enter "Disk Management." If you see the Extend Volume option grayed out on your computer, there is no unallocated space on your hard disk.

4. How do you add space to the C drive?

  • Launch EaseUS Partition Master.
  • Right-click on the System C: drive and select "Resize/Move".
  • Drag the system partition end into the unallocated space.
  • Click "Apply" to execute the changes and extend the C drive.

Was This Page Helpful?

Updated by Oliver

Oliver is an EaseUS professional writer who dares explore new areas. With a passion for solving tech issues with straightforward guides for common users, Oliver keeps honing his writing craft by developing in-depth solutions for disk and partition management, computer boot-up issues, file transfer, etc.

Read full bio

Written by Tracy King

Tracy became a member of the EaseUS content team in 2013. Being a technical writer for over 10 years, she is enthusiastic about sharing tips to assist readers in resolving complex issues in disk management, file transfer, PC & Mac performance optimization, etc., like an expert.

Read full bio