Running low on disk space on your Mac?

Here is how to find out what uses up the most disk space on macOS Mojave without installing any 3rd party app.

Dennis Schäfer
Mar 21, 2019 · 7 min read

It’s no secret that disk space for Macs is expensive. For example, if you decide to purchase a 13" MacBook Air with 256 GB SSD, you have to pay an additional $200 / 250 € compared to the 128 GB SSD model. Although, you can use cloud storage services like Dropbox, Box, iCloud and alike, you will quickly reach the limits with 256 GB and even quicker with 128 GB, in particular when taking a lot of photos or videos. Usually, macOS will confirm this by telling you Your startup disk is almost full.

Calculate All Sizes

I have a 13" MacBook Pro with a 512 GB SSD and recently noticed that there is only ~60 GB of free space left, so I wanted to know where and how that disk space is used. The obvious solution however, the folder size column in Finder, didn’t show anything by default.

Finder’s size column doesn’t show the folder size by default

In order for this column to work, I had to activate size calculation for folders. This setting can be found in View — View Options (⌘J).

Check Calculate all sizes to display the folder & file size in Finder.

Your Finder window has to be in List View for the Calculate all sizes option to be available, as only this view option displays folder sizes. Each view has their own options. After activating this option, the size column in Finder shows now the actual disk space used.

The size column displays the current folder size.

The problem with this option to find out what uses up your disk space is, that it can be quite a tedious task to go through all folders. In addition, your system might use some significant space for cached files, e.g. mail or iMessage attachments that are not easy to find and navigate to using Finder. There are certainly 3rd party apps that can help de-cluttering your file system and help freeing up space. However, in this article I want to explain how to achieve similar results by using built-in functionality of macOS.

Manage Disk Space

Since macOS Sierra (the version before High Sierra and Mojave), there is the System Information app that allows you to better manage your disk space. You can launch it by clicking  — About This Mac — Storage.

About This Mac shows how much disk space is free.

The colored bar shows you which file category uses how much data. File categories are for example Documents, Apps, Photos, iTunes, System, and a few others. Hovering over the colored bar will show a little tooltip with category name and the space it currently uses. However, the real power of this app is shown, when you click the Manage… button.

This will open a new window, that gives you a whole lot of options to optimise your disk space. At the very top is Recommendations, which is subdivided into Store in iCloud, Optimise Storage, Empty Trash Automatically and Reduce Clutter. These are pretty basic recommendations.

Apple’s recommendation to easily free up some disk space.

Store in iCloud:

All messages and attachments will be stored in iCloud. When storage space is needed, only recent attachments will be kept on this Mac. You can download attachments at any time.

You can modify this preference later in Messages Preferences.

Store all files, photos and messages in iCloud and save space on your Mac. You’ll see one or more of the following options, based on how you’ve set up storage management in iCloud, Photos and Messages.

  • Desktop and Documents: Store all the files from your Desktop and Documents folders in iCloud Drive and optimise storage by keeping only recently opened files on your Mac when storage space is needed.
  • Photos: Store your photo library in iCloud and optimise storage by keeping only optimised photos and videos on your Mac when storage space is needed.
  • Messages: Store all messages and attachments in iCloud and keep only recently opened items on your Mac when storage space is needed.

Optimise Storage:

When storage space is needed, films and TV programs in iTunes that you’ve already watched will be automatically removed and only recent email attachments in Mail will be kept on this Mac. You can download them at any time.

Optimise Storage offers these two options to activate:

  1. Automatically remove watched iTunes films and TV programs
  2. Download only recent attachments / Don’t automatically download attachments

The last one is a bit unusual, because it is implemented with a checkbox for a drop-down.

Unusual way of implementing the optimise storage option.

By the way, clicking on the ? for help will only bring up one single help page — Store in iCloud (as described above).

Empty Trash Automatically:

This option allows you to turn on automatic deletion of all files that have been in Trash for more than 30 days. This setting can also be activated in Finder Preferences — Advanced.

Reduce Clutter:

Clicking on Review Files… will just jump to Documents in the sidebar left.

Applications, Documents, Messages

Located below Recommendations on the left there are probably some of the most common categories where you find items that use up your disk space. It’s really handy to see all those categories with the space they use. Selecting one of those categories, e.g. Applications, will display more details as well as some actions in the view on the right. Sorting by size will quickly reveal the big boys. Then you can decide whether to you want to keep the app or delete it straight from there.

The Applications category displays all installed apps.

One thing I found strange is the value of size attribute, because it’s in some instances significantly different to the calculated size in Finder (e.g. Xcode 6.5 GB difference). I didn’t dig deeper into that, as it already helped me finding unused apps to be deleted regardless of their size. However, here is the comparison between Finder and the System Information app. You can see how the Microsoft Office apps for macOS are much bigger and are listed above GarageBand in Finder.

Xcode is 6.5 GB larger in Finder than in System Information.

The Documents section is subdivided into three subcategories: Large Files, Downloads and File Browser.

Large Files is really handy as it does something that Finder cannot do. It provides at list of all large files in the Documents folder regardless how well hidden they are in subfolders.

Documents displays a list of all large files on your disk.

The Downloads folder is probably one of those locations where a lot of files just sit there and waste space. So, it absolutely makes sense to be reminded to look into this folder every now and then and check which files can potentially be deleted. The key difference to directly looking into the Downloads folder in Finder is that here, the files are sorted by the date they were last accessed (e.g. 3 months, 6 months, older than 1 year).

The File Browser gives you a Column View, which displays the folder/file size. Finder cannot display the size attribute in the Column View.

If you use iMessage on your Mac, you have probably tried deleting message attachments once and noticed that there is no simple and convenient way to do so. You can find the location of the attachment by CTRL-clicking on the attachment, e.g. an image, and select Services — Show in Finder. But this doesn’t bring you to a single folder where all attachments are stored. No, iMessage attachments are stored in many different folder. That’s where the Messages category will help you, because it displays all locally cached attachments sorted by size or last access date and allows you deleting them from there.

Easily find all attachments from iMessages.

There are a lot of other categories to explore. For example, iOS Files allows you to quickly delete local backups of your iOS devices, Music Creation allows you to purge all sound library items of GarageBand in one go and Mail allows you to only download recent attachments.

At the end of the day, the manage storage feature of the system information app gives you a holistic view of where and how your disk space is used and provides you with an overarching interface to clean-up actions that are otherwise hidden in macOS.

How do you usually keep your Mac clean? Do you use any 3rd party apps or are you using the tools available on macOS?


The official Apple knowledge base article about optimising storage in macOS Sierra:

Taggy Tagger — a Finder tag manager for macOS. —

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