---
id: mac-storage-basics.why-is-a-folder-a-different-size-on-another-drive
url: https://storagestudio.us/faq/mac-storage-basics/why-is-a-folder-a-different-size-on-another-drive
category: "Mac storage basics"
subcategory: "Finding big files, Downloads and the Trash"
question: "Why is a folder a different size after I copy it to another drive?"
alt_questions:
  - "folder bigger on external drive"
  - "copied folder size different mac"
  - "size changed after copy"
  - "exfat folder bigger"
  - "files take more space on external 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."
tags: ["file size", "copy", "formats"]
related: ["https://storagestudio.us/faq/mac-storage-basics/why-does-get-info-show-size-and-on-disk", "https://storagestudio.us/faq/mac-storage-basics/what-format-works-on-both-mac-and-windows"]
applies_to: "all"
last_reviewed: 2026-10-01
---

# Why is a folder a different size after I copy it to another drive?

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.