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[Allocation Unit Size FAT32 Guide] What Allocation Unit Size Should I Use for FAT32

Updated by Daisy on Feb 22, 2023
Written by Tracy King

When you buy a new USB flash drive or SD card, usually you don't think about formatting. But formatting the flash drive is actually a wise and necessary process. To make it simple, formatting your USB flash drive or SD card has two advantages. First, it prepares your drive for proper use by your computer. Second, it creates a filing system that makes your data organized while allowing you to store the most files possible.

While formatting your flash drive, you need to choose a proper allocation unit size (also known as cluster size). The different file system has different allocation unit size. In this article, we will tell you what allocation unit size you should choose for FAT32.


  1. 1. How to Check Allocation Unit Size
  2. 2. What Allocation Unit Size Should I Use for FAT32
  3. 3. Bonus Tip: How to Convert FAT32 to NTFS with Partition Manager

How to Check Allocation Unit Size?

The allocation unit size, which is also called cluster size, is the block size on the hard drive when formatting FAT32, exFAT, or NTFS. A hard drive is divided into clusters. the size of the allocation unit demonstrates the size of a single cluster. When you format a partition, the file system which you use keeps a track of clusters. Whenever a file or a piece of a file is written on any cluster, it is considered occupied.

To check the allocation unit size of your USB drive or SD card, you can apply the following steps.

Step 1. Connect your flash drive to the computer. Open File Explorer.

Step 2. Right-click your USB flash drive, choose "Format".

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

Check allocation unit

See Allocation Unit Size FAT32: What Allocation Unit Size Should I Use for FAT32?

Sometimes, users need to convert NTFS to FAT32 or convert FAT32 to NTFS for USB flash drives. Changing the file system of a drive means you should change the allocation unit size, too. But what is the proper allocation unit size for FAT32? Don't worry, we will tell you the answer.

The allocation unit size does not only depends on your file system but also depends on the size of your USB flash drive or SD card. For FAT32 drives, the default cluster size on Windows 10 is as follows.

Volume Size Default Allocation Unit Size
32 MB–64 MB 512bytes
64 MB–128 MB 1 KB
128 MB–256 MB 2 KB
256 MB–8GB 4 KB
8GB–16GB 8 KB
16GB–32GB 16 KB

1 KB equals 1024 bytes. Generally, a common USB flash drive is larger than 2 GB. If your USB flash drive is smaller than 8GB, the most proper allocation unit size is 4096 bytes. If your flash drive is larger than 8GB but smaller than 16GB, the most proper allocation unit size is 8192 bytes. If your flash drive is larger than 16GB, the most proper allocation unit size is 16 kilobytes.

For NTFS drives, the default cluster size on Windows 10 is as follows.

Volume Size Default Allocation Unit Size
7 MB–512 MB 4 KB
512 MB–1 GB 4 KB
1 GB–2 GB 4 KB
2 GB–2 TB 4 KB
2 TB–16 TB 4 KB
16TB–32 TB 8 KB

Bonus Tip: How to Convert FAT32 to NTFS with Free Partition Manager

FAT32, exFAT, and NTFS are all file systems that are applied in Windows operating system. The file system provides a way to organize drives. It specifies how the data is stored on the drive and what types of information can be attached to the file-file name, permissions, and other attributes.

Among the three mentioned file systems, NTFS is the most modern one. It's more efficient and supports a big feature set. So in some cases, users might need to format their flash drive from the old FAT32 to the newer NTFS. To perform such a process, we'd like to introduce a free tool for you - EaseUS Partition Master Free.

This free tool is designed for partition management. You can resize your partition, fix C drive out of space, convert FAT32 to NTFS, and merge partitions with EaseUS Partition Master Free. Now, please download the EaseUS Partition Master Free from the button below, and follow the guide to see how to convert FAT32 to NTFS.

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Step 1. Install and launch EaseUS Partition Master on your computer.

Step 2. On Partition Manager, right-click on a FAT32 partition and click "Advanced", select "NTFS to FAT".

convert FAT32 to NTFS

Step 3. Click "Proceed" on the pop-up dialog box to continue.

convert FAT32 to NTFS

Step 4. Click "Apply" to start the converting process. Wait until the operation process is finished.

convert FAT32 to NTFS

The Bottom Line

Hope this article could solve all your questions about "what allocation unit size should I use for FAT32". Generally, the allocation unit size of FAT32 drives ranges from 4KB to 16KB. You can select the appropriate size by referring to the table in this article. What's more, if you are interested in converting FAT32 to NTFS, you can download EaseUS Partition Master Free and have a try.

PAA about Allocation Unit Size FAT32

What allocation unit size should I use for FAT32 32GB?

For FAT32 32GB drives, you can set the allocation unit size as 16KB.

What is the best cluster size for FAT32?

When it comes to FAT32, the best cluster size varies depending on the hard drive and the purpose of the partition. A cluster size is simply a group of sectors with a minimum and maximum number of bytes that make-up a single file system allocation unit. Generally, smaller cluster sizes equate to more efficient use of hard drive space. For FAT32, most systems default to the best cluster size being 4KB (4096 bytes). Some systems may be able to use a 16KB or 32KB best cluster size for larger partitions.

What allocation unit size should I use?

If you are a beginner, the default 4096 bytes is the standard allocation unit size.

What is allocation unit size for 32GB SD card?

The allocation unit size of a 32GB SD card can vary quite significantly depending on the type of card being used and how it was formatted but is generally between 16KB and 32KB.

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About the Author

Updated by Daisy

Daisy is the Senior editor of the writing team for EaseUS. She has been working in EaseUS for over ten years, starting from a technical writer to a team leader of the content group. As a professional author for over 10 years, she writes a lot to help people overcome their tech troubles.

Read full bio

Written by Tracy King

Tracy joined in EaseUS in 2013 and has been working with EaseUS content team for over 10 years. Being enthusiastic in computing and technology, she writes tech how-to articles and share technical solutions to resolve Windows & Mac data recovery, data backup, partition management, data transfer, Windows update issues, etc.

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  • Partition Master Free can Resize, Move, Merge, Migrate, and Copy disks or partitions; convert to local, change label, defragment, check and explore partition; and much more. A premium upgrade adds free tech support and the ability to resize dynamic volumes.

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  • It won't hot image your drives or align them, but since it's coupled with a partition manager, it allows you do perform many tasks at once, instead of just cloning drives. You can move partitions around, resize them, defragment, and more, along with the other tools you'd expect from a cloning tool.

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