How to Add Unallocated Space into Partition in Windows 10 Successfully?

This post explains how to add unallocated space in Windows 10 via Disk Management. Besides, we also share a great tool just in case that you can't add unallocated space as expected.


By Emily / Updated on April 16, 2024

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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 partition 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. In such cases, adding unallocated space into that partition can help extend the capacity and solve the low disk space issue.

Add Unallocated Space to Partition in Windows 10 via Disk Managment

There are more than one way for you to add unallocated space to a partition, but the most frequently-used should be built-in Disk Management that is able to delete, extend, create, and format partitions. You can enter the tool by right-clicking This PC > Manage > Disk Management.

To add unallocated space, you just right-click the partition that is adjacent to the space on the left side and select "Extend Volume".

Extend Volume

Select the disk that contains the unallocated space, and follow the prompt to merge the unallocated space into the selected volume.

Select Unallocated Space

Can't Add Unallocated Space Windows 10, Why?

Although the process seems to be quite simple, there is one thing we should keep in mind: the unallocated space can only added to the partition on its left side and adjacent to it.  That's why some users report that they cannot combine unallocated space with existing partition in Windows 10 and the Extend Volume greyed out.

Extend Volume Greyed Out

Besides, 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 Grey out

Easier Way to Add Unallocated Space to Partition without Restrictions

From above, it is easily concluded there are many limitations when you use the Disk Management to add unallocated space into other partitions. So, here we would like to share you with an easier way to do such tasks. That is using a 3rd-party disk partition management tool: AOMEI Partition Assistant Standard Edition.  Its "Merge Partitions" feature allows you to add unallocated space into any partition (without losing any data) regardless of whether it is right behind the target partition or not, or they are the same partition type (primary partition and logical partition).

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

Download Freeware Win  11/10/8.1/8/7/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 AdvancedMerge Partitions (e.g. C partition).


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


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


Merging partition is not the only way to add unallocated space into 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 upgrade to professional and 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 11/10/8/7. 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 and more. If you are a computer user who wants to safely manage their partitions in Windows Server 2022, 2019, 2016, 2012, 2008 and 2003, then AOMEI Partition Assistant Server is the software for you.

Emily · Staff Editor
Emily is an English editor of AOMEI Technology; she has a great passion for providing easy solutions for people to tackle with all disk or partition management problems. In addition to writing articles about disk/partition management, she also edits great tutorials on how to back up and restore disk for data security. In her spare time, she loves to learn computer skill to improve herself or stay with her family to enjoy a good day.