By AOMEI / Last Updated April 9, 2021

Why Need to Add Unallocated Space in Windows 10 Partition?

Unallocated space is the disk space that doesn’t belong to any partition and no programs or data are allowed to write to it. This type of space can be used to store deleted files, but when Operating System saves another file in the same place, the previous data will be overwritten. To take full advantage of all your storage space, computer users can either add unallocated space to a partition in Windows 10, or create a new partition with the unallocated space.

However, the majority of users want to add unallocated space to another partitions in Windows 10. Over time a number of files will build up on your system that will eventually use up a large amount of space. This could lead to a "low disk space" warning on your system partition and makes computer slow down. Most users will experience this issue soon or later, so how do we fix it?

Of course, there is a method for you. That is adding unallocated space into partition windows 10, which means that you can extend partition with unallocated space. And then you can solve the low disk space in Windows 10.

How to Add Unallocated Space in Windows 10 Partition?

There are two common ways for you to add unallocated space to a partition. One is via the Windows 10 Disk Management tool, the other is via third-party software.

1. Add unallocated space to a contiguous partition via Disk Management

Disk Management is a built-in tool in Windows 10 that is able to delete, extend, create, and format partitions. You can enter the tool by right-clicking This PC > Manage > Disk Management. When there is unallocated space next to the partition you want to add the unallocated space into, just right-click the partition and choose Extend Volume.

If the unallocated space shown in Disk Management is in the extended partition, then you will not be able to add it to your primary partition even if they are contiguous (please see this guide to move Free space out extended partition). As well as this, you will also be unable to add any unallocated space to a logical partition.

Extend Volume Greyed out

If the unallocated space is not adjacent to the partition you want to add to, then the Extend Volume option will be grayed out. In the screenshot below you can see that the Extend Volume option has been grayed out in the popup menu as there is no unallocated space next to the C partition on Disk 0.

So, why does this happen? The Extend Volume function will only be enabled when there is unallocated space next to the primary partition (ie: target partition) or free space next to a logical partition.

Therefore, if you want to use Windows Disk Management you should make sure your partitions are compatible beforehand. If your partitions aren’t compatible and you want to add unallocated or free space to any partition, we would recommend using a specialist third party tool.

2. Merge unallocated space to any partition via 3rd party software

AOMEI Partition Assistant Professional Edition is a powerful partition management tool, which can help you manage your partitions safely and efficiently. Using its "Merge Partition" feature, you can add unallocated space into any partition (without losing any data) regardless of whether it is right behind the target partition or not.

PS.: You can download the demo version to experience a simulation!

Download Free Demo Win 10/8.1/8/7/XP
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Step 1: Install and run it. Right-click the partition you want to add the unallocated space to and then choose Merge Partitions (e.g. C partition).

Merge Partition

Step 2: Select the unallocated space and then click OK.

Check Unallocated Space

Step 3: In the pop-up window, you will realize the size of partition has been increased. To perform the operation, please click Apply.

Apply Merge Partitions

Merging partition is not the only way to add unallocated space to a partition. To add unallocated space to another non-adjacent partition, you can also first move the partition between the aim partition and unallocated space to the right side, and then extend the partition with adjacent unallocated space.

Move Partition

Besides, if there is no unallocated space on the disk for extending another drive, you can make use of the "Allocating Free Space" function to directly add free space from one partition to another partition.

Allocate Free Space


This specialist software makes it much more convenient and simpler than ever before to add unallocated space into another partition in Windows 10/8/7 and Windows XP/Vista. Apart from resizing partition flexibly, this software is also able to clone partition, clone hard disk, migrate only OS drive to SSD/HDD, convert MBR and GPT without deleting partitions, convert dynamic disk to basic one without deleting volumes, and more.

If you are a computer user who wants to safely manage their partitions in Windows Server 2019, 2016, 2012, 2008 and 2003, then AOMEI Partition Assistant Server is the software for you.