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What is the difference between “Size” and “Size on disk?”

Fresh7 days ago
Mar 15, 2026247224 views
Confidence Score1%
1%

Problem

Looking at the properties for a Windows file I get two attributes, “Size” and “Size on disk,” and "Size on disk" is always larger. What do these two metrics mean?

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Fix for: What is the difference between “Size” and “Size on disk?”

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Size is the actual size of the file in bytes. Size on disk is the actual amount of space being taken up on the disk. They differ because the disk is divided into tracks and sectors, and can allocate blocks of discrete size. For a more detailed explanation, see this text which I copied from another site: We know that a disk is made up of Tracks and Sectors. In Windows that means the OS allocates space for files in "clusters" or "allocation units". The size of a cluster can vary, but typical rang…

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