What Is the Best Allocation Unit Size for USB When Formatting: 2024 Guide

Wondering how to pick the best allocation unit size USB when formatting? In this article, we will tell you what is the best allocation unit size for USB flash drives, how to check USB allocation unit size, and how to change the size. A safe way to convert USB between FAT32 and NTFS without losing data is also covered here.


By Phoebe / Updated on March 27, 2024

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What is the best allocation unit size for USB flash drive?


I'm currently transferring music MP3 files to a 32 GB thumb drive and have had to reformat the thumb drive multiple times during the troubleshooting process I'm working on. I don't know how to choose the allocation unit size wisely, and why. Are there any tutorials/blogs that can provide insight into these formatting options?"

- Windows Ten Forums

When you format a new storage device, whether designated for games, videos, or music, you will be prompted to select an allocation unit size. But what does this term actually mean?

The allocation unit size, also known as the cluster size or block size, represents the smallest unit used to store and manage files on disk. Hard drive storage within a computer is organized around these clusters. It is worth noting that the size of the allocation unit can significantly affect the performance of the storage device.

USB drives are widely used for storage, data backup, and file transfer between devices in our daily life and work. Choosing the right size for your USB drive is critical to ensuring the best user experience.

But what is the best allocation unit size USB? The default allocation unit size depends not only on your file system but also on the capacity of your USB flash drive. Popular file systems in Windows are FAT32, NTFS, and exFAT, macOS uses APFS and HFS+, and Linux uses EXT. This article will delve into the nuances of FAT32, exFAT, and NTFS tailored specifically for Windows systems.

Let's have a detailed look:

File system format

Partition size

Default allocation unit size


7 MB - 16 TB

16 TB - 32 TB

32 TB - 64 TB

64 TB - 128 TB

128 TB - 256 TB

256 TB - 512 TB

512 TB - 1 PB

4 KB (4096 Bytes)

8 KB

16 KB

32 KB

64 KB

128 KB

265 KB


32 MB - 64 MB

64 MB - 128 MB

128 - 256MB

256MB - 8GB

8GB - 16GB

16GB - 32GB

512 bytes (0.5 KB)

1 KB

2 KB

4 KB

8 KB

16 KB


7MB - 256MB

256MB - 32GB

32 GB - 256 TB

4 KB

8 KB

16 KB

How to check allocation unit size USB

After knowing which allocation unit size to choose for your flash drives, the next step is how to check allocation unit size USB. Refer to the following steps:

Step 1. Connect your USB flash drive to the computer and make sure it can be detected. Double-click on My Computer/This PC to open File Explorer.

Step 2. Right-click your USB flash drive and select Format.

Step 3. Under the drop-down menu of Allocation Unit Size, you can see the allocation unit size of your USB drive now.


How to change USB allocation unit size

After going through the best allocation unit size USB, users may need to change it on their system based on the file size through formatting. This section will offer three ways to change USB allocation unit size: via Disk Management, via DiskPart, and via a third-party formatter. If you want to format a partition larger than 32GB to FAT32, move directly to the way 3.

Tip: The formatting process will delete all data on the USB, please back up important data before reformatting to ensure data security or move some installed games to another drive.

Way 1. Change USB stick allocation unit size with Disk Management

You can change the allocation unit size USB Windows 10/11 through Disk Management (DM).

Step 1. Right-click the Start icon and click Disk Management.

Step 2. Find the target USB partition (for example, H:) where you want to resize the cluster. Right-click on it and select Format....

Step 3. In the prompted formatting window, find the Allocation unit size (cluster size) option. Here we select 64K.

Step 4. Check Perform a quick format box and click OK to start the formatting process.


Way 2. Change USB stick allocation unit size with DiskPart

You can also change cluster size through DiskPart:

Step 1. Press the Windows + R keys together to open Run box. Type diskpart and hit Enter.

Step 2. Input the following commands and hit Enter after each command line:

▶ list disk

▶ select disk 1 (Replace 1 with the disk containing your USB.)

▶ list partition

▶ select partition 1 (Replace 1 with the target partition to format.)

▶ format fs=fat32 (Replace fat32 with the needed file system to format.)


Step 3. When the formatting process is completed, type exit to close the window.

Way 3. Change USB stick allocation unit size with a third-party formatter

Although Windows DM and Diskpart can help you change the cluster size for storage devices, you may encounter problems when using them. For example, when you want to change the allocation unit size USB 64GB as FAR32 with DM, the FAT32 option might not be available. Then you may resort to Diskpart, you will encounter the "Virtual Disk Service error: The volume size is too big." message. That is because the default Windows formatting tools do not allow users to format partitions larger than 32GB to FAT32.

In this case, you can also use a free 3rd party partition manager - AOMEI Partition Assistant Standard to change cluster size in Windows 11/10/8.1/8/7. it can help you change block size for USB drives, SD cards, and external/internal hard drives through its "Format Partition" function. It shows great advantages in formatting drives, especially in formatting devices larger than 32 GB as FAT32.

With its user-friendly interface and detailed operation guidance, you can format drive to Ext4/Ext3/Ext2, FAT32, exFAT, and NTFS with easy clicks.

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Follow the below steps to see how to change USB allocation unit size exFAT/FAT32/NTFS and more:

Step 1. Install and start AOMEI Partition Assistant Standard.

Step 2. Right-click on the USB drive. Then choose Format Partition.


Step 3. You can add a partition label. Here we set the file system as FAT32. Click OK to continue.


Step 4. Click OK > Proceed to execute the operations. Once the process has been completed, your USB drive now operates with the FAT32 file format.

Tip: You can recover data from formatted drives if you upgrade to its Pro edition.

Bonus tip: How to convert USB between FAT32 and NTFS without data loss

As mentioned previously, changing the USB stick allocation unit size and file system by formatting will delete all data stored on it. There is a way to change the file system without data loss. If your USB comes per-formatted as the NTFS or FAT32 file system, there's an option to directly convert the file system between NTFS and FAT32 without formatting the USB.

Download the demo version and have a try.

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Here we take the conversion from NTFS to FAT32 as an example.

Step 1. Start AOMEI Partition Assistant Professional.

Step 2. Navigate to Convert > Convert to NTFS/FAT32 in the taskbar.


Step 3. In the prompted window, select NTFS to FAT32 and click Next.


Step 4. Locate and select your USB drive. Click Next.


Step 5. Click Proceed to confirm the operations. After completion, click Finish.


Final words

How to choose the allocation unit size USB depends on its file format and storage capacity. Guess now you have learned the details. If you want to format a USB larger than 32GB as FAT32, you can use the AOMEI Partition Assistant.

Besides formatting and converting the file system, this program also enables you to allocate free space to game drives, safely upgrade HDD to SSD for disk upgrades, and convert MBR to GPT disk format without data loss. The Server edition is designed for the Windows Server system.

Phoebe · Staff Editor
Phoebe, an editor at AOMEI Technology, is dedicated to offering optimal solutions for Windows-related concerns, specializing in partition management, disk upgrades, data recovery, and more. During her free time, she enjoys indulging in reading, watching movies, and exploring her passion for cooking.