By Bryce / Last Updated March 10, 2022

Why format unallocated disk?

Unallocated space is the free storage on your disk that has not been in use. It can be used by putting system to put files on but there is no application that can write to it. It is a waste to leave unallocated space on your disk alone. Your disk is not allocated, that is to say, there is no partition and there is only unallocated space on your disk. At this point, to make full use of your disk, it is fairly necessary to format it with a certain file system.

How to format unallocated disk using CMD?

Diskpart is Windows 11/10 built-in disk partition management command-line tool that can help you to create partition, format partition, delete partition, and so on. You can use this tool to format unallocated disk easily and quickly. Here are detailed steps (Take formatting unallocated disk using CMD in Windows 11 as an example):

1. Press Windows + R at the same time to open Run box.

2. In the Run box, type diskpart in the Run box and hit Enter key to run Diskpart utility.

3. In the Diskpart window, type the following commands one by one and press Enterafter every command.

▪ list disk – to list all disk in the current system
▪ select disk m – m is the number of the unallocated disk that you need to format
▪ create partition primary
▪ format fs=fat32 – you can replace this command with format fs=ntfs or format fs=exfat based on your need
▪ assign letter f – f can be replaced by other letter if you want

How to Format Unallocated Disk using CMD

Now, your unallocated disk has been formatted and you’ll able to see the partition on it in Windows File Explorer.

Unable to format unallocated disk space

According to aforementioned, we can realize how to format unallocated disk using CMD in detail. However, you are not allowed to create partition on unallocated space on SD card or USB flash drive when it has hold one or more partitions; If you do that using Diskpart utility, you’ll receive the error message that “No usable free extent could be found. It may be that there is…”. You are also unable to format unallocated disk space larger than 32GB as FAT32 file system; when you format partition over 32GB as FAT32 via Diskpart, you’ll be prompted by the message that the volume size is too big.

In view of the above, it is recommended to turn to third party partition software to format unallocated disk (space).

Unable to Format Unallocated Disk Space

Volume Is Too Big for FAT32

Free yet powerful 3rd party partition manager: AOMEI Partition Assistant Standard

Here AOMEI Partition Assistant Standard will be my first choice, which is compatible with Windows 11/10/8.1//87, XP and Vista. It supports formatting large unallocated disk space to FAT32 and create second partition on SD card or USB flash drive with the unallocated space. And it allows you to format unallocated disk to FAT32, NTFS, exFAT, Ext2, Ext3, and Ext4, so that your disk can work with different operating systems and electronic devices.

Step 1. Connect your disk to the working computer and ensure that it can be detected. Then, download freeware AOMEI Partition Assistant.

Download Freeware Win 11/10/8.1/8/7/XP
Secure Download

Step 2. Install and run AOMEI Partition Assistant. In the main interface, find out the unallocated disk that’ll be formatted, right click the unallocated space on it and choose “Create Partition”.

Creat Partition 16GB

Step 3. In this small pop-up window, you can specify the size and location of the new partition; assign a drive letter to it; choose the file system of it. Here NTFS is selected. Then, click “OK” to continue.

Edit New Partition OK

Step 4.Here you’ll return to the main interface where you can preview your operation. Then, click“Apply”>“Proceed” to perform it.

Proceed Create Partition 16GB


▪ For step 3, if the drive letter of the partition is set as “None”, you’ll not be able to see it in Windows File Explorer.

▪ For step 3, if you need to create partition on SSD, it is advised to tick the box before “SSD Partition alignment" under Advanced tab.


It’s an easy task to figure out how to format unallocated disk space using CMD. However, it is more advisable to try this third party partition manager – AOMEI Partition Assistant Standard out of its powerful functions and simple operation.

Apart from the functions mentioned above, AOMEI Partition Assistant Standard owns many other functions. And my favorite one is the Migrate OS to SSD function that helps me to upgrade my hard drive to SSD without the trouble of reinstalling operating system. And if you need to migrate OS from MBR disk to GPT disk, you can upgrade AOMEI Partition Assistant to Professional version.