Size Vs Size on Disk Difference in Windows Explained

Jack Rayan

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Many users have noticed that when they look at a file’s properties, the Size and Size on disk values are different. This is usually not a problem, but it can cause some confusion when trying to understand what’s going on. So, what is the difference between these two values? This article will explain why this happens and how to calculate the real Size.

The actual file size

When you look at the properties of a file, folder, or drive, you can see the size of each in terms of bytes. The actual file size represents the byte count of the data that is stored inside each file and folder. The size of the files and folders also depends on the allocation unit size (cluster size). The cluster size determines the amount of space that is allocated for each file. Different cluster sizes waste or save disk space.

As an example, a 1 KB file saved on a drive with 32 KB clusters will actually take up 32 KB on the disk. This is because the files are kept in sectors that are close to each other on the hard disk. When a file is defragmented, it spreads out across the hard disk. This decreases the overall size of each file and increases its performance. This is why it’s so important to maintain a regularly-defragmented hard drive.

The file system’s allocation unit size (cluster size)

When you view a file’s properties, it shows two sizes—Size and Size on disk. The latter reflects how much space the file is taking on the storage drive and includes details like the file system’s allocation unit size (cluster size) and disk storage format. A larger cluster size means more wasted space. This is because the data in a file is written in sets of clusters that have different sizes. A set might be 4 KB, 32 KB or 64 KB in size.

Allocation unit size, cluster size and block size are all synonymous and refer to the chunks that a solid state or hard disk drive is divided into. Each file uses a minimum of one cluster for each byte of information it contains, regardless of its actual size. That’s why you might see a large discrepancy between the File Size and the File Size on Disk value in Windows. This is why many tools, such as help to describe what a file is using.

The format of your storage disk

When you’re looking at the properties of a file or folder, you see two different values: Size and Size on disk. The Size value shows the actual size of the file, and the Size on disk value indicates how much space it occupies on your hard drive. The Format of your storage disk is another factor that can affect the Size on disk value. When you save a file, the operating system divides it into clusters (small data units). Each file takes up multiple clusters, which increases the size of its Size on disk value.

You can check the Format of your storage disk in Windows by using the Disk Management utility. Open it by right-clicking the My Computer icon on your desktop and selecting Manage in the context menu. The Disk Management window will appear with a pie chart that illustrates information about the selected disk or partition. To get the most accurate result, select the disk or partition containing the file or folder that you’re examining.

The number of small files

When you look at a file or folder’s properties, you might notice that the Size and Size on disk numbers are different. This is because Windows uses two different calculations to determine the size of a file or folder. The first, Size, represents the actual amount of data a file or folder contains. This is the number you see in the properties window when you click “Size.”

The second, Size on disk, combines a few different factors to calculate how much space a file or folder takes up on your storage disk. These factors include the file system’s allocation unit size (cluster size) and your storage disk’s format.

The difference between Size and Size on disk can be confusing, especially when you see a huge discrepancy between the two values. However, the key to understanding these differences is knowing what each term means and how they are calculated. Once you understand this, you’ll be able to make sense of the Size vs Size on disk difference.

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