By Teresa / Last Updated November 19, 2020

Why move unallocated space to C drive?

Unallocated disk space refers to the unused hard drive space on your disk. It won’t show up in Windows Explorer, yet you can check if you have unallocated space in Disk Management by typing “diskmgmt.msc” in “Run” box. Moving unallocated space to C drive in Windows 10, 8, 7 is good way to enlarge system drive, so that you can install more programs there and keep other programs function well. The performance of your system drive will directly affect the function of the OS and software, games in particular. More free space makes creating personal files easier.

Some computers come with small-sized system partition when produced by manufacturers. If there is plenty of free space in other partitions like D, E, you can allocate free space from each partition to C drive directly. All in all, you may hold other factors that force you to extend the system drive. The most important thing is to find how to move unallocated space to C drive using the simplest method.

How to allocate unallocated disk space to C drive in Windows 10/8/7?

The method you choose to add unallocated space to C drive is determined by the location of unallocated disk space. Generally speaking, you have three ways to complete this task, built-in Disk Management, Diskpart and third-party software.

1. Add unallocated space to C drive in Disk Management

As covered before, the location of the unallocated space affects your choice. If it is next to C drive and at its right side, you can add it to system (C:) drive directly in Disk Management. Open Disk Management, right click C drive and select “Extend Volume” in the menu. The only thing left to do is following the wizard to resize system partition.


2. Transfer unallocated space to C drive via Diskpart

Likewise, you can directly extend C drive to the unallocated space when the space is adjacent to C drive on its right side. Let’s get to know how to work this out using CMD.

1. Press Windows key plus R key to open Run. Type diskpart and press Enter. Run as administrator.

2. Type following commands in turn and each command has an Enter followed by.

  • list volume

  • select volume c (or select volume 1)

  • extend (or extend size=10240 which means you’ll extend by 10GB in size)

  • exit

Diskpart Extend C Drive

This is how to move allocated space to C drive via Windows built-in tools. But they can only work when the unallocated space is adjacent to the C drive on the right side. If the unallocated space is separately distributed on the hard drive, for example, the unallocated space after D drive in the screenshot, you will find the “Extend Volume” grayed out in Disk Management, and you’ll get Diskpart failed to extend the volume error in Diskpart.

Extend Volume Grey Out

In those situations, you need to delete the in-between partition, extend C drive and then restore the partition. So, is there any way to move unallocated space to the right side of the C drive and extend it successfully? Luckily, the last method can help you out.

3. Move unallocated space to C drive via free partition manager

To add unallocated space to C drive flexibly, you can try the free partition software: AOMEI Partition Assistant Standard. Its “Move Partition” feature can help you move the unallocated space to the right side of the C drive, and then you can extend the target partition easily. Besides, the “Merge Partitions” can directly merge all unallocated space on the hard drive to C drive without formatting or deleting partitions even when the unallocated space is not contiguous to the primary drive.

It has graphical and clean user interface and is suitable for all PC users varying from novices to professionals. Download and learn how to merge unallocated space to C drive in Windows 10, for instance.

Step 1. Install and start AOMEI Partition Assistant Standard. Right click C drive and select “Merge Partitions”.


Step 2. Tick all unallocated space you want to add into C drive and click on “OK".


Step 3. Confirm the virtual outcome. Click “Apply” to execute the operation.


Since there is system drive involved in this operation, it will complete allocating in restart mode. Moreover, you can upgrade to Professional edition, which provides more better ways to extend partition: “Allocate Free Space” allows you to directly transfer some space from one partition to another by 3 steps and the “Extend Partition Wizard” helps you to exend NTFS system drive without rebooting computer.

Allocate Free Space


Believe it or not, you can easily move unallocated space to C drive in Windows OS with AOMEI Partition Assistant. You have options to merge data partitions (say D, E drive) to system drive as you wish using the same feature. As a matter of fact, it can do many other things, for example, it enables you to install Windows 10 on external hard drive and realize BYPD with “Windows to go Creator” wizard. When upgrading hard drive, the “migrate OS to SSD” wizard matters a lot.To add unallocated space to C drive in Windows Server 2008/2003/2012/2016/2019 without deleting, please refer to AOMEI Partition Assistant Server Edition.