Frequently Asked Questions

WhatSize 7.3.3 Now supporting macOS Catalina (10.12 and above)
Re-engineered using the latest Apple technology

Or you can always start a free trial!

What is WhatSize?

WhatSize is a FileSystem utility that lets you view and clean up files and folders based on size. The application is optimized to quickly measure the size in bytes of a given folder or of an entire FileSystem. Once a measurement has taken place, the user can view, filter, sort, and remove files and folders that are taking up too much space.


Our software is signed with Apple to comply with the GateKeeper Technology.


Since version 6.1.4 our software is compiled as a 64 bit. Yes it will use more memory but the benefits are far greater.


We are fully suporting hfs, and its variants, which covers 99% of file system types on the mac. SMBFS or windows shared volumes are not supported on 6.1.4 but might be added very soon.

The Mac App Store version?

It is pretty much the same binary as the one you download from us except we are not allowed to support any of the features that require Administrator(sudo) privileges such as Measure as Administrator or Find File Duplicates, Move to Trash as Administrator.
These features are great in case you are administering multiple users on the machine, a good example is kids. If you are the only user of the machine than the AppStore version is fine.
We will continue to support both the App Store and the GateKeeper version for the forseable future. If you want the App Store version you will have to repurchase using your Apple ID.

How are Time Machine volumes supported?

Time Machine uses hard links to speed up and limit the amount of data on backups. We will not measure or modify Time machine volumes currently but plan to support them in the near future.

How are the files sizes calculated?

WhatSize measures the Physical and Logical size of each file and displays the Physical size. This is actually the proper way to show how much disk space a file is using. This is the same value you see when you perform "Get Info" on a file in Finder.

The Block size is the smallest chunk of information the operating system will use to store data. The default is usually 4KB, but this value can vary between 4KB to 256KB.

The Logical size is the actual size of the file, regardless of Block size.

As an example, if you create a simple text file with one character in it, the file’s Logical size will be one byte (1B), but because the Block size is 4KB, the Physical size of the file - the actual space used on your hard drive to store this file - is 4KB.

How are folder sizes calculated?

WhatSize takes into account the folder size itself and thus the WhatSize measurement is a bit bigger than the Finder’s. The folder size is what the file system is reserving for the folder itself. For example, a folder with 25,000 zero size files will still take roughly 1MB. The 1MB is used by the Operating System behind the scenes to manage the folder contents.

How can I view the file size of several selected files?

As of 4.9.8, in all views, you can select the files and use the keyboard shortcut Cmd + I (that is a letter capital i, not the number 1). In the Table View, you can also right-click and choose "Selection Size".

Can I measure as an Administrator?

Yes. Click on "Measure as User" in the toolbar to toggle between measuring as a User or the Administrator To measure as administrator, the application will bring up the System Administrator panel and upon authentication as Administrator will spawn a background process that runs as sudo to measure all files on a given Volume/Folder regardless of permissions. This is useful when measuring an entire Volume. The background process will quit when the measurements are completed or the main application quits.

What are Apple's FSEvents

Apple technology that allows applications to synchronize with file system changes in real time. One of the most famous users of this technology is TimeMachine. Using this technology will allow WhatSize to stay up to date with file system changes and open the door for some nifty features in the very near future.

What is a bit, a byte, a kilobyte, a megabyte, etc?

- One Bit is one tiny piece of information.
- One B (Byte) = Eight Bits
- One KB (Kilobyte) = 1024 Bytes (2 to the 10th power)
- One MB (Megabyte) = 1024 KB = 1,048,576 Bytes (A CD is usually around 600 MB)
- One GB (Gigabyte) = 1024 MB = 1,073,741,824 Bytes (A DVD is usually around 4.5 GB)
- One TB (Terabyte) = 1024 GB = 1,099,511,627,776 Bytes (About 230 DVDs or 1,750 CDs)
- One PB (Petabyte) =1024 TB = 1,125,899,906,842,624 Bytes (About 230,000 DVDs or 1,790,000 CDs)

Why are the measured free GB’s so different from Finder.app?

Finder displays the available space on the disk without accounting for the local snapshots. A clean reboot will allow Finder to be accurate.

Finder displays the size without taking into consideration resource fork data.
WhatSize does not have permission to measure files and folders owned by other users of the machine. You need to 'Measure as Administrator'. Contact Us if you want to replace the Mac App Store version.

Why is my brand new 150GB external hard drive only showing 139GB available?

It’s because drive manufacturers use the decimal system to measure drive capacity (in which 1 GB = 1,000,000,000 bytes, not 1024^3 bytes). Apple switched to using this method in their Snow Leopard release (so in Snow Leopard a 150 GB drive shows up at 150 GB. So this is not an issue when using SnowLeopard and newer.

I accidentally deleted a file. How can I recover it?

Open up the Trash and move the file back to its proper location.

I lost my license email. How can I register my copy of WhatSize?

We’re working to automate this, but for now please email whatsize at id-design.com with the email address you used to purchase the license.

Is quicklook enabled?

As of 4.9.8, yes, simply select a file and hit the spacebar just like in Finder.

How do I enter the license info manually ?

Please consult the User Guide.

I have an old computer

Download the latest version that runs on Mac OSX 10.11 (El Capitan)

Download the latest version that runs on Mac OSX 10.6 (Snow Leopard)

Download the latest version that runs on Mac OSX 10.5 (Leopard)
Download the latest version to run on Mac OSX 10.4 (Tiger) (PPC & Intel)

Or you can always start a free trial!