How to Know the Size of a Folder in Windows 10

Steps to Find the Folder Size in Windows 10

1. Right-click on the folder you want to find the size of.
2. Click on the Properties.
3. Look for the label Size and Size on disk.

That’s it. It will list the size of the folder both in MBs and bytes. You should only look at the Size value, not the Size on the disk. The Size is the actual size of your file. But why are the values of Size and the Size on the disk showing differently? Read more in the following section.

Size vs Size on disk

Short answer: The size is the actual size of the file and the Size on the disk is the amount of space it takes to store it on your hard drive.

Long answer: The hard drives are made of tracks and sectors. The operating systems including Windows 10 allocate the space for the files to reside in “allocation units” or “clusters. An allocation unit will only contain a single file even though the size of the file (or part of the file for larger files) is less than the allocation unit. A typical allocation unit can be anywhere from just 512 bytes to 32,000 bytes. This means, let’s say the current allocation unit size of your drive is 4096 bytes (a standard allocation size for drives). Even if the file is less than 4096 bytes, the entire 4096 bytes will be allocated for that single file. For example, a file with 2500 bytes in size will also take 4096 bytes to be stored in the hard drive.

For larger files, a portion of the file will also consume some unused space. Let’s say I have a file with the size 22 KB. It will need 6 allocation units (6 x 4096 = 24,576 bytes) to store the file even though the actual size of the file is just 22,000 bytes. Because 5 allocation units will only have 20,480 bytes that is not enough to store the entire file. So, the rest of the space where the last chunk of the file is stored will be added to the “size on the disk”. So, that’s why the size on the disk will be always greater than the actual size of the file unless you are using some compression mechanisms.