By Cherry / Last Updated February 7, 2020

About cluster size

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 organized 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 why 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, the 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 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 a better performance.

How to change cluster size of volume?

Change cluster size of volume requires volume reformat, which would delete all data on the partition. Thus, you need to backup partition before changing cluster size. Here provides you three ways to change cluster size of volume:

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 needs to change to, here is 64 kilobytes, selectQuick 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, typecmd in the search box, run the program as administrator.

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

Step3. Type list disk.

Step 4. Type select disk 2.

Step 5. Type list partition.

Step 6. Type select partition 1.

Step 7. Type format fs=ntfs unit=64k.

* Each step will be executed after pressing Enter key. So you need to press Enter after each command.

Diskpart Change Cluster Size

3. Free tool to change cluster size

Besides Windows File Explorer and Diskpart, you can also use a free tool to change cluster size. AOMEI Partition Assistant Standard is such a great free tool that can help you change cluster size through Format Partition function.


  • Change cluster size through Format Partition will lose data on the volume. If you want to keep the old data, you can use the AOMEI Partition Assistant to store the data on another place first. This free software provides you copy partition wizard which you can use to copy partition before formatting it. Thus, when you change cluster size of volume through formatting partition, the data will be safe in another place.

  • After changing cluster size, you can use it as a new partition.

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.

Partition Label

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


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


This article provides you three methods for how to change cluster size. No matter using Windows built-in tool or third party software, you can choose the one which is suitable for you. As for AOMEI Partition Assistant, it is not only a free tool that can help you change cluster size, but also a disk partition manager that can help Windows 7/8/10 users settle many disk partition problems like repartition hard drive, convert FAT32 to NTFS without 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.