{"id":"comparisons.duplicating-in-finder-vs-copying-to-another-drive","url":"/faq/comparisons/duplicating-in-finder-vs-copying-to-another-drive","category":{"id":"comparisons","title":"Comparisons & alternatives"},"subcategory":{"id":"files-and-formats","title":"Files, links and archive formats"},"question":"Why doesn't duplicating a big file in Finder use more space, but copying it to another drive does?","alt_questions":["APFS clone vs copy","duplicate file on Mac doesn't use extra space","why did Duplicate not reduce my free space","copy to external drive takes full space","what is an APFS clone"],"short_answer":"On APFS, a Finder Duplicate is a clone that shares the original's data, so it uses almost no extra space at first. Copying to another drive writes the full size, because nothing can be shared across drives.","answer_markdown":"On an APFS drive, Finder's **Duplicate** (and copying within the same volume) makes a *clone*: the copy shares the original's data until one of them is edited, so it uses almost no extra space at first. Copying to a different drive can't share anything, so the full size is written there.\n\nTwo consequences worth knowing:\n\n- Deleting one of a pair of clones frees little or no space, because the other still holds the shared data.\n- Edits to a clone gradually use real space, as the changed parts are stored separately.\n\nThis is also why moving a folder to your external drive only frees space on your Mac once the original is gone — the data has to physically live on the other drive. See [why free space didn't go up after a move](/faq/moving-folders/why-didnt-my-free-space-go-up-after-a-move).","answer_html":"

On an APFS drive, Finder's Duplicate (and copying within the same volume) makes a clone: the copy shares the original's data until one of them is edited, so it uses almost no extra space at first. Copying to a different drive can't share anything, so the full size is written there.

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Two consequences worth knowing:

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This is also why moving a folder to your external drive only frees space on your Mac once the original is gone — the data has to physically live on the other drive. See why free space didn't go up after a move.

","answer_text":"On an APFS drive, Finder's Duplicate (and copying within the same volume) makes a clone: the copy shares the original's data until one of them is edited, so it uses almost no extra space at first. Copying to a different drive can't share anything, so the full size is written there.\n\nTwo consequences worth knowing:\n\n- Deleting one of a pair of clones frees little or no space, because the other still holds the shared data.\n- Edits to a clone gradually use real space, as the changed parts are stored separately.\n\nThis is also why moving a folder to your external drive only frees space on your Mac once the original is gone — the data has to physically live on the other drive. See why free space didn't go up after a move.","tags":["apfs","clone","finder","free space"],"related":[{"id":"comparisons.symbolic-link-vs-alias-vs-hard-link","question":"What's the difference between a symbolic link, an alias and a hard link on a Mac?","url":"/faq/comparisons/symbolic-link-vs-alias-vs-hard-link"},{"id":"comparisons.moving-vs-deleting-to-free-space","question":"Is it better to move files off my Mac or delete them?","url":"/faq/comparisons/moving-vs-deleting-to-free-space"}],"applies_to":"all","last_reviewed":"2026-10-01","title":"Why doesn't duplicating a big file in Finder use more space, but copying it to another drive does? — Storage Studio FAQ","description":"On APFS, a Finder Duplicate is a clone that shares the original's data, so it uses almost no extra space at first. Copying to another drive writes the full size, because nothing can be shared across drives.","crumbs":[{"name":"Home","path":"/"},{"name":"FAQ","path":"/faq/"},{"name":"Comparisons & alternatives","path":"/faq/comparisons/"},{"name":"Why doesn't duplicating a big file in Finder use more space, but copying it to another drive does?","path":"/faq/comparisons/duplicating-in-finder-vs-copying-to-another-drive"}],"jsonld":{"@context":"https://schema.org","@type":"FAQPage","url":"https://storagestudio.us/faq/comparisons/duplicating-in-finder-vs-copying-to-another-drive","inLanguage":"en","dateModified":"2026-10-01","mainEntity":[{"@type":"Question","name":"Why doesn't duplicating a big file in Finder use more space, but copying it to another drive does?","alternateName":["APFS clone vs copy","duplicate file on Mac doesn't use extra space","why did Duplicate not reduce my free space","copy to external drive takes full space","what is an APFS clone"],"acceptedAnswer":{"@type":"Answer","text":"On an APFS drive, Finder's Duplicate (and copying within the same volume) makes a clone: the copy shares the original's data until one of them is edited, so it uses almost no extra space at first. Copying to a different drive can't share anything, so the full size is written there.\n\nTwo consequences worth knowing:\n\n- Deleting one of a pair of clones frees little or no space, because the other still holds the shared data.\n- Edits to a clone gradually use real space, as the changed parts are stored separately.\n\nThis is also why moving a folder to your external drive only frees space on your Mac once the original is gone — the data has to physically live on the other drive. See why free space didn't go up after a move.","url":"https://storagestudio.us/faq/comparisons/duplicating-in-finder-vs-copying-to-another-drive"}}]},"fragment":"
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Comparisons & alternatives · Files, links and archive formats

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Why doesn't duplicating a big file in Finder use more space, but copying it to another drive does?

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Short answer: On APFS, a Finder Duplicate is a clone that shares the original's data, so it uses almost no extra space at first. Copying to another drive writes the full size, because nothing can be shared across drives.

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On an APFS drive, Finder's Duplicate (and copying within the same volume) makes a clone: the copy shares the original's data until one of them is edited, so it uses almost no extra space at first. Copying to a different drive can't share anything, so the full size is written there.

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Two consequences worth knowing:

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  • Deleting one of a pair of clones frees little or no space, because the other still holds the shared data.
  • Edits to a clone gradually use real space, as the changed parts are stored separately.
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This is also why moving a folder to your external drive only frees space on your Mac once the original is gone — the data has to physically live on the other drive. See why free space didn't go up after a move.

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Last reviewed

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Related questions

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