Mac storage basics · Finding big files, Downloads and the Trash
Why is a folder a different size after I copy it to another drive?
Short answer: Different block sizes, APFS clones and compression that don't carry over, online-only files being downloaded, or sparse files expanding. Check the file counts match.
Usually because the drives store files differently:
- Block size: a format with larger blocks (common on exFAT drives) makes many small files take more space.
- Clones and compression on your Mac's APFS drive save space that a copy to another drive doesn't keep.
- Online-only cloud files may be downloaded during the copy.
- Sparse files can expand when copied by some tools.
The file count should match; if it doesn't, the copy may be incomplete.