What Is Allocation Unit Size for an SD Card? Everything You Need to Know

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The smallest unit of data that can be stored on your storage disk is referred to as "cluster size." To elaborate, when you save a file onto your storage device, its size is determined by the allocation unit size you set. As you increase the allocation unit size, the file size on the disk will also increase.

There is no doubt that allocation unit size influences the speed of file access, the size of files, and the amount of space utilized on your SD card and USB. When your computer writes or reads a file, it does so within these allocation units. Hence, specifying a larger allocation unit size will cause the file to occupy fewer units, thereby enhancing the file access speed by your operating system.

What is the allocation unit size for an SD card? This article will provide all the information you need. Keep reading!

What Is Allocation Unit Size for SD Card?

You can observe that there are numerous options available for the allocation unit size when formatting an SD card, USB flash drive, or external hard drive partition in Windows 11, 10, 8, and 7. These options span from 4K to 64 KB.

Then, which one is the best for your SD card? The allocation unit size has minimal impact on the performance of an SD card. When formatting, you can often just choose the default allocation unit size. Typically:

• For SD cards with 32GB capacity or less, choose the file system FAT32 and an allocation unit size of 32 KB.
• For cards with 64GB storage and above, select the file system exFAT and an allocation unit size of 128 KB.

Utilizing different allocation unit sizes is not equivalent. Smaller allocation unit sizes can lead to increased time spent accessing data, whereas larger sizes can result in wasted disk space and increased wear and tear. If you intend to store only a few small files on the SD card, a smaller size might be appropriate. However, if you need to store numerous large files, such as video files, a larger allocation size could enhance read and write speeds.

For more information on allocation unit size, like the optimal SSD cluster size, please refer to the following article:

What's The Optimal SSD Allocation Unit Size in Windows 11/10

On this page, we will discuss the optimal SSD allocation unit size for Windows 11/10. Additionally, you'll find the best approach to modify it.

How to Check Your Allocation Unit Size for SD Card

By now, you should have a thorough understanding of the allocation unit size in an SD card. To address your question on how to check the allocation unit size for your SD card, you can utilize the Diskpart tool. Here are the steps to do so: 1. Press the Windows key + X on your keyboard and select "Command Prompt (Admin)" or "Windows PowerShell (Admin)" to open an elevated command prompt. 2. Type "diskpart" and hit Enter. This will launch the Diskpart utility. 3. Once inside Diskpart, type "list disk" and press Enter. This will display a list of all disks connected to your system, including your SD card. 4. Identify your SD card from the list by looking at the "Size" column. Note the disk number (usually Disk 1, Disk 2, etc., depending on the other storage devices connected). 5. Type "select disk [disk number]" (replace [disk number] with the actual number of your SD card) and press Enter. This selects the SD card for further operations. 6. Now, type "detail partition" and press Enter. This command will show detailed information about the partitions on the selected SD card, including the allocation unit size. The allocation unit size will be listed as "Allocation Unit Size" or "Cluster Size." That's it! You've successfully checked the allocation unit size of your SD card using Diskpart.

Step 1. Make sure the SD card or USB device is connected to the computer.

Step 2. In the Search bar, type diskpart, right-click the most relevant result, and select Run as administrator. Next, in the User Account Control (UAC) window, click Yes to proceed.

Step 3. Enter the following commands one by one in the elevated diskpart.exe window, pressing Enter after each command to execute it:

Step 4. As shown in the screenshot below, you can now view the current allocation unit size for your USB or SD card, along with the default sizes for various file systems.

How to Alter Allocation Unit Size for an SD Card

From the above two parts, we know the appropriate allocation unit size for an SD card and how to check the clusters of an SD card. If your cluster size doesn't meet your requirements, you might need to change it. Adjusting the exFAT or FAT32 allocation unit size is essential for optimizing partition efficiency. The tools Partition Master is a powerful tool that enables you to assign the unit size effortlessly.

As a professional disk partition tool, you can easily and quickly modify the cluster size. It allows you to adjust the allocation unit size of the SD card without any risk of data loss.

Step 1. Right-click the partition whose cluster size you need to change, select "Advanced" and click "Change Cluster Size".

Step 2. Click the size list under the New Size section, and select the desired cluster size you want to adjust for the disk partition, then click "OK".

Step 3. Click "Execute 1 Task(s)" and then "Apply" to confirm the action.

Partition Master is a comprehensive tool with numerous features, allowing you to easily perform tasks such as changing SSD cluster size.

Conclusion

In summary, we have comprehensively addressed the question "what is allocation unit size for SD Card." We have outlined various methods for setting the allocation unit size for an SD card. Feel free to select the method that best suits your needs for allocating the unit size.

Moreover, we suggest giving the tool Partition Master a try to allocate the unit size for your SD card. It facilitates easy allocation of unit size for SD cards, cloning system partitions, merging partitions, and is compatible with Windows 10, 11, 7, and 8. Download Partition Master and give it a shot yourself!

Frequently Asked Questions About Allocation Unit Size for SD Card

After reading this post, you already have the answers. If you have any suggestions regarding this topic or if you have any questions, please feel free to leave them in the comments section.

1. What is allocation unit size when formatting an SD card?

The size of a cluster in hard drive partitions refers to the allocation unit size. Clusters serve as the fundamental unit of storage organization on a computer's hard disk. For instance, if you have a 4097-byte file and the cluster size is 4096 bytes, the file would need to be saved across two clusters, consuming a total of 8192 bytes. Conversely, if the cluster size is 512 bytes, the file would require storage in nine clusters, occupying a total of 4608 bytes.

2. What allocation unit size should I use?

The ideal allocation unit size for your drive often depends on your disk size and operating system. A single movie file usually ranges from several hundred MB to a few GB, so using a larger allocation unit size is logical if, for example, you have a partition or drive dedicated solely to movies. You could opt for the maximum 2MB allocation unit size, but keep in mind that this will cause smaller files, like subtitle files, to occupy the minimum amount of that space.

3. What is the allocation unit size for a 128 GB SD card? The allocation unit size, also known as the cluster size, for a 128 GB SD card typically ranges from 4KB to 64KB. The exact size depends on the file system used, with newer file systems like exFAT or NTFS tending to have larger allocation units compared to older ones like FAT32. To determine the specific allocation unit size for your 128 GB SD card, you can use tools like Windows' Disk Management or third-party utilities.

USB allocation unit size for 128GB: 8096 (8kb) For a 512GB USB, the allocation unit size is 32k. For USB drives exceeding 512GB, the allocation unit size is 64k or larger. For a 256GB USB, the allocation unit size is 16k. When the USB flash drive is formatted as exFAT and has a capacity above 64GB, the system automatically sets the allocation unit size to 8096 (for 128GB), 16K (for 256GB), and 32K (for 512GB).