How to find what's using disk space on a Mac: Free up space

Apple MacBook base models have limited storage space and it is easy to fill small drives. Some MacBooks have 128 GB SSDs, which can cause serious space problems. Find and clean space hogs.

Hard disk drives teadily increased in size over time and storage space problems disappeared. However, the switch to solid-state drives (SSDs) had a serious affect on space a drives dropped to just 64 GB. Yes, the MacBook Air a few years ago had just 64 GB of storage space. There should not be many of those models till running, but even today, there are MacBooks being sold by Apple with just 128 GB SSDs.

That is a very small amount of storage for a modern computer that works with apps, games, digital photos, movies, TV shows, podcasts and music. Even if you pay extra for a bigger drive when you buy your Mac (don't under estimate storage requirements), you could still run out of space.

If the Mac's drive is nearly full, what can you do? Obviously, you need to delete files to free up space, but which ones? Being able to see which files and folders use the most space is essential and it is pointless deleting small files that use little space.

Here we look at a couple of ways to see what is using the most disk space. They enable you to instantly see which folders and files are using the most storage space and knowing this, you can then do something about it, such as deleting big files or moving them to external storage like a USB disk drive.

First we will look at features built into macOS and then use a free utility called OmniDiskSweeper.

View space usage using macOS features

Go to the Apple Menu and select About This Mac. Select the Storage tab and all the drives, internal and external, are listed. You can easily see how much free space is on each drive and by letting the mouse hover over a coloured section of the space usage bar, you can see what is using the space.

It depends on your MacBook, but it can take a minute or two to produce the results. It does not provide any details, so you don't know exactly what is using the space. It is too general to enable you to take any action to free up space. Click the Manage button.

This is more useful and the sidebar breaks down the drive space usage by category. It does not show files or locations and Documents for example, refers to files you created and not the Documents folder on the disk.

Select Documents in the sidebar.

Files are displays and they are sorted by size, with the largest first. The location is not displayed, but only files in your home folder are shown, which narrows it down a little. There is a separate tab to show Large Files or Downloads. Unsuported apps, like 32-bit ones in macOS Catalina, can be displayed too.

This file display does not show everything on the Mac, but it does show the most important. Select a file and there is an button at the bottom of the window to delete it.

Some of the other categories in the sidebar are useful and if you never use GarageBand for example, you can free up a couple of gigabytes of disk space by removing the sound files and tutorials. They can be downloaded again if you ever need them.

Managing the disk contents using the features built into macOS is useful for some things, but not for others. It can also be quite slow to navigate, sometimes taking a minute or so to scan the drive and update the view. OmniDiskSweeper is an alternative.

View space usage using OmniDiskSweeper

OmniDiskSweeper is a free utility that enables you to explore the disk drive and view the folders and files it contains. It scans the disk, sorts everything by size, and let's you browse the results and see what is using the most space. Space hogging files and folders can be removed.

Download OmniDiskSweeper and double click the .dmg file to open it. Drag the app to the Applications folder to install it. It is a small app that uses little disk space itself.

Run OmniDiskSweeper and macOS security kicks in. It will not let you run it straight away because it did not come from the Apple Mac Store. However, this app is completely safe, so ignore the warning and open it anyway.

A list of the internal and external disk drives attached to the Mac is shown and you just click the one to explore. Wait! Quit and open System Preferences > Security & Privacy. Select the Privacy tab and then select Full Disk Access on the left. Tick OmniDiskSweeper.app on the right to give it full disk access. (Don't forget to click the padlock in the bottom left corner and enter your admin password.)

Now you are ready to run OmniDiskSweeper. It displays a small window containing all the internal and external drives. Double click a drive to begin exploring it. Notice that the space usage of any drive can be explored, not just the Mac's internal drive. You can just as easily explore a USB drive and manage the space on it, which macOS About This Mac will not lt you do.

A new window opens and t slowly builds up a list of the folders and sizes. It can take a minute or two to do this and little appears to be happening on the screen, so be patient.

Once it has finished, the folder that is using the most disk space is at the top of the first column, with increasingly smaller folders and files below. It works just like Finder’s column view and selecting a folder in the first column displays the contents in the next one. Selecting one there, shows its contents in the next and so on. Just drill down to see what is using all the storage space.

The folder and file sizes enable you to view the amount of space required and the colour coding shows very large items, medium size and small items. This view of the disk contents enables you to quickly find the largest folders and files in a way that would be difficult with Finder. In some ways, this is similar to About This Mac, but you can see file and folder locations, and it works with external drives too.

There are few features, but there is a delete button if you find files and folders that you want to remove. A better way to deal with space hogs though, is to double click the folder. This opens it in Finder and you can then choose how to deal with it, such as deleting it or moving it to external storage.

OmniDiskSweeper is an old utility that has been around for years, but it is free and it is still very useful. There is a Catalina/Mojave version and other versions for older macOS releases. It is so important with today’s MacBooks with small solid state disks that easily run out of storage space.