If your Mac is starting to run slow the first thing to check is if you are running low on space. It's generally advised that you should have 10% of your total space free on your Mac for the most optimum working. If you are down to your last few GB then it's time to do some house work and grab yourself some space back. 

Over time, a Mac's hard drive is likely to accumulate a large collection of duplicate files that take up this valuable space so that's a good place to start. However, finding and deleting them can be time-consuming if you do it one by one, so in this article we show you quicker ways to cleanse your system of these delinquent doppelgängers.

Why do I have duplicate files?

In most cases these will be mistaken downloads (caused by clicking on a link twice), Mail and Messages attachments, or a number of other possibilities. Unless you're an unusually fastidious Mac user, duplicates are going to turn up one way or another.

Manually searching for duplicates with Finder

It is possible to locate duplicate files on your system by using the Smart Folders feature in Finder.

How to find and delete duplicate files on Mac: Finder Smart Folders

  1. Start by opening the Finder app.
  2. Navigate to File > New Smart Folder.
  3. Click on the '+' button in the upper-right corner.

Now you can search for documents, photos, music, or several other files types. The key is how you sort the results. Ordering them by name should bring up any duplicates that are easy to spot.

How to find and delete duplicate files on Mac: Smart Folders

Just remember to check the date to see if it is a true duplicate - you don't want to delete the wrong version of an important document, for example.

While this is doable, it's far from ideal. The time spent ploughing through the long list of files could be better spent by visiting the App Store and buying software that will do the process for you instead.

Using dedicated third-party apps

There are a number of duplicate file finders on the Mac App Store which will automatically search your system and recommend file doubles that can be removed.

Many are free, including Duplicate File Finder Remover and Duplicates Cleaner. You could also try the Find Duplicates feature of Parallels Toolbox, which offers a free trial.

Most offer similar features, in that you ask the app to scan your hard drive, then are presented with a list of duplicates, accompanied by the original file so you know which ones are safe to delete.

How to find and delete duplicate files on Mac: Duplicate File Finder

Usually you'll have to move to a paid version for advanced features such as deleting duplicate folders, hidden files and similar functions.

One of our favourite apps, and one with a good level of positive feedback from customers, is Gemini 2: The Duplicate Finder, which is free to download but offers a Smart Cleanup feature for £19.99/$19.99 as an in-app purchase. While the name might be more in keeping with a dystopian sci-fi novel, the app is a powerful tool for your Mac.

Not only can it find doubles of any files on your hard drive, but it also searches external drives and cloud storage services such as Google Drive and Dropbox. All this is accompanied by the ability to immediately replace any accidentally deleted files.

Read more about Gemini - and the firm's other related apps, such as CleanMyMac X - on MacPaw's website.

All of the apps listed above will certainly clear up some space on your Mac, and you can always start with the free ones then move up to a paid version later if you find the features useful.

For more decluttering tips, be sure to read our How to free up space on a Mac feature, and a separate article that explains how to empty the Trash on your Mac. We also have advice about how to remove duplicated music in iTunes (or the Music app).

We also have this guide to ways to speed up a slow Mac and How to delete Other storage on the Mac and an article that explains How to delete cache on a Mac.