How to Recover Unallocated Space on USB Flash Drive?

Why USB drive lose space?

When trying to use your USB drive, you plug it in your computer and open My Computer, only to find that much space on the USB drive is lost, leaving only a few megabytes available free space. Then you open Disk Management, which is a Windows built-in utility, to see what really happens to your USB drive. You will find out that the lost space is shown as unallocated. Before you manage to recover unallocated space on the USB drive, you may want to know how this happened. The lost space on USB drive often occurs after trying to burn a system to the USB drive. Some operating system (OS), such as Chrome OS and Linux, will change the partition system of your removable device, so there will be little free space on your USB drive. Using some third party software inappropriately or an unsuccessful formatting may also cause inaccessible portion on your USB drive, which is shown as unallocated space.

Disk Management

How to use the unallocated space?

When this situation happens to you, there is no need to worry, because there are many ways to solve the USB drive showing less space error. The most simple and effective method is using Disk Management. In case you delete something essential to your system, Disk Management cannot delete or format some system related files, so you may find there is no way to put the unallocated space in use. Then you can switch to another tool named Diskpart that can definitely help you to reclaim the lost space on your USB drive. Before you get started, backup data because incorrectly operations with Diskpart may cause permanently data loss.

Step 1: connect the USB drive you are having a problem with to your computer, and type “diskpart” in the Run dialog or search box, and press Enter to open Diskpart utility.


Step 2: Run "list disk" command to display all the online disks with a specific disk number on your computer.

Step 3: Run "select disk <disk number>" to select the USB drive. From here, the disk number of the USB drive is 2, so just type "select disk 2" command.

Step 4: Type "clean" to delete all volumes and partitions on the selected disk, which is the USB drive from here.

Step 5: type "create partition primary" to create a primary partition. If you want to create more than one partition on the USB drive, you specify the partition size referring to the following syntax: create partition primary [size=n]. For example, to create a 3000MB partition, run this command "create partition primary size=3000".

Recover Unallocated Space

After a little while, Diskpart will succeed in create a partition. Then you can format unallocated space on your USB drive easily. Since this method involves complete deletion of your USB drive and all the operations cannot be canceled or undone, be extra careful while you do it. If you are not familiar with Diskpart, you can also use a free partition manager with a clear interface to do this.

How to recover lost space with third party partition software?

AOMEI Partition Assistant Standard edition is a free partition manager software for Windows 10/8/7. With its concise interface, you can use it to take control of all the space on your USB drive.

1. Free download this software, install and launch it.

2. In the main interface, right click on the existing partition on your USB drive and select “Format Partition”. In the next pop-out window, select NTFS or FAT32 as its file system and click “OK” to proceed.

Format Partition

3. Right click on the existing partition and select “Resize partition”. In the next screen, drag the slider to the end of the disk so that all the unallocated space will be added into the partition.

Extend Partition

4. At this point, you can preview partition status or undo any operations. If no problem, just click Apply to apply the changes.


In a few seconds, AOMEI Partition Assistant will recover unallocated space on USB drive. If your USB drive is larger than 16GB, you can use the Quick Partition feature to quickly repartition your drive. If you happen to delete one partition unintentionally, you can use the Partition Recovery Wizard to help you get your data back. As an extraordinary partition manager, AOMEI Partition Assistant also provides the ability to convert NTFS to FAT32 without data loss, migrate OS to SSD, make bootable media, and many more.