How to find and delete duplicate files on a Mac

Every Mac collects duplicates. A file gets downloaded twice, a photo gets exported to three folders, a project gets copied before a risky change and never deleted. Individually they are small. Together they can take tens of gigabytes, and they are the safest thing on your drive to remove because you keep a copy by definition.

Where duplicates come from

A few habits produce most of them.

• Downloading twice. Safari and Chrome add "(1)" and "(2)" to the name and keep both.
• Exporting photos and videos. Photos, Lightroom, and screen recorders all write to whatever folder was last used, so the same clip ends up in Desktop, Downloads, and Movies.
• Copying folders as a backup. "Project copy", "Project old", and "Project FINAL" all live side by side.
• Cloud sync conflicts. Dropbox, Google Drive, and iCloud create "conflicted copy" files when two devices edit the same document.
• Installers and disk images. The same .dmg gets downloaded again every time an app needs reinstalling.

Why name matching is not enough

Finder can sort by name, but two files with the same name are not always duplicates, and two duplicates rarely share a name. A proper duplicate finder compares content. DiskDude's Duplicates view hashes files and groups those with identical bytes, so IMG_4021.jpg and beach trip.jpg are matched if they are the same picture, while two different files called notes.txt are left alone.

Finding them in DiskDude

1. Scan the folder you want to check. Your home folder is a good starting point.
2. Open the Duplicates view. Groups are sorted by how much space you would recover, largest first.
3. Expand a group to see every copy and its full path.
4. Pick the copies to remove and add them to Cleanup. DiskDude always leaves at least one file in each group.
5. Review the Cleanup list and remove the files.

Which copy should you keep?

There is no single rule, but these guidelines work well.

• Keep the one in the folder where you would look for it. A photo in Pictures is easier to find later than the same photo in Downloads.
• Keep the one inside a synced folder if you rely on iCloud Drive or Dropbox for backup.
• Keep the original, not the export, when the original is a project file that can produce the export again.
• Delete the copy in Downloads in almost every case.

What not to deduplicate

Some duplicates are there on purpose.

• Application bundles often contain the same library several times. Leave /Applications alone.
• Photos libraries and other packages manage their own contents. DiskDude treats them as single items for this reason.
• Git repositories store copies of files in .git. Deleting them breaks the repository.
• Time Machine and backup folders are supposed to duplicate your files.

Stick to your own documents, media, and downloads and you will recover space without breaking anything.