By Cherry / Last Updated March 17, 2022

What does cluster size mean?

According to Wikipedia, a computer cluster consists of loosely or tightly connected computers that work together so that, in many respects, they can be viewed as a single system. Unlike grid computers, computer clusters have each node set to perform the same task, controlled and scheduled by software.

As we all know, cluster is the smallest unit to save and manage files in disk in Windows OS. One cluster can only hold one file even if it is only one byte. When you need to save small files, you need to configure a volume with small clusters, which can improve disk space use ratio. While if you need to save large files, the volume should be appointed with large clusters, which can optimize data read-write speed largely.

Why do you need to change cluster size?

A hard disk partition can be formatted to NTFS, FAT, exFAT. All file systems that are used by Windows operating system to organize your hard disk base on cluster size (also known as allocation unit size). If you haven’t specified cluster size when you format a partition, it will select the defaults based on the size of partition. And this is one of the reasons for which you need to change cluster size of volume.

Different file system has different default cluster size. Thus, if you format partition from FAT to NTFS, you may need to change cluster size. By default, the maximum cluster size for NTFS under Windows NT 4.0 and later versions of Windows is 4KB. Imaging that if you use Convert.exe utility to convert a FAT to NTFS, Windows always uses the original FAT cluster size as the NTFS cluster size for cluster size up to 4KB. If the FAT cluster size is greater than 4KB, then, the clusters are converted down to 4KB in NTFS.

In common, 512b cluster is the old generation standard, 4k cluster is more common today, 64k cluster size is for big file storage like game, 3D movie, HD photo. You can change cluster size according to the file size for better performance.

3 Free tools to change cluster size of volume

Many Windows users want to change cluster size without formatting. However, reformatting the volume is the only method to change allocation unit size by far, so it is not possible to change (NTFS) cluster size without formatting. But, we can back up important data before reformatting it so as to ensure data security. When the backup is done, you can use the following free tools to change cluster size in Windows 11/10/8/7.

1. Change cluster size in Windows File Explorer

You can change cluster size through Windows File Explorer.

Step 1. Press Windows + E keys simultaneously, right-click on the partition you want to change cluster size, select Format... Here we take G: for example.

Step 2. Click Allocation Unit Size (Cluster size), select one cluster size you need to change to, here is 64 kilobytes, select Quick Format Start.

Allocation Unit Size

It will show you a format warning message, click YES to continue. After a while, the format complete, and you have already changed the cluster size.

2. Change cluster size with Windows Diskpart

You can also use “format fs=ntfs quick unit=64k” command to accomplish the operation.

Step 1. Click Start button, type cmd in the search box, run the program as administrator.

Step 2. when the command prompt pops up, type diskpart and press Enter key to open the diskpart command prompt.

Step3. Type list disk and press Enter.

Step 4. Type select disk 2 and press Enter.

Step 5. Type list partition and press Enter.

Step 6. Type select partition 1 and press Enter.

Step 7. Type format fs=ntfs unit=64k and press Enter.

Diskpart Change Cluster Size

3. Freeware to change cluster size

Besides Windows File Explorer and Diskpart, you can also use a 3rd party partition manager to change cluster size. AOMEI Partition Assistant Standard is a recommended free partition manager that can help you change cluster size through “Format Partition” function.

Note: To keep the old data, you can use the AOMEI Partition Assistant to store the data on another place first. Its copy partition wizard allows you to copy partition to another partition before formatting it. Thus, when you change cluster size via formatting partition, the data will be safe in another place.

Download Freeware Win 11/10/8.1/8/7/XP
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1. Free download AOMEI Partition Assistant, install and launch it. To change cluster size of a partition, right-click it, select Format Partition.

Format Partition

2. In the format partition window, you can edit partition label, select file system, and change cluster size in the drop-down menu. Click OK. Here we change cluster size from 4k to 64k.

Change Cluster Size

3. Here you will back to the main interface, click Apply to execute the whole operation.


Wait till the progress reaches 100%. close the program to quit it.


This article provides you three free tools for how to change cluster size. No matter using Windows built-in tool or third party software, you can accomplish this task easily. As for AOMEI Partition Assistant, it is not only able to change cluster size for free, but also can help Windows 11/10/8/7 users settle many disk partition problems like repartition hard drive, convert FAT32 to NTFS and NTFS to FAT32 without reformatting or losing data, etc. You can even upgrade to AOMEI Partition Assistant Professional edition to unlock more advanced features such as Allocated Free Space, partition alignment, change partition type ID, etc.