MacOS – How to see how much storage is used per app on OS X

I have a 128GB Air with Lion and iLife '11 ... which is what, by default, would come on a new Air from the Apple Store or authorized reseller. I have other apps, so this is only a guess, but...

• Lion: 4-5 GB
• iLife '11: 5 GB
• Recovery Partition: 650 MB

So, on a 128GB Air, you should see about 115-118GB free space. On a 256GB Air, you would see about 243-246GB free space.

Other is a catch-all by taking the drive's max capacity and subtracting the sum of all other counted file sizes. So, if your drive has corruption where many blocks are unavailable or lost, you will see large other "allocations".

If the other space remains the same after running disk utility to verify and/or repair the volume then you can assume it's really files taking that space.

The categorization comes from spotlight indexing, so you could search here how to rebuild that index if you suspect bad metadata leading to an incorrect storage report.

The simplest way to rebuild the metadata (spotlight) index is to simply add your hard drive to the spotlight privacy list in system preferences and subsequently remove it. The built-in help should have a guide if you're not sure how to refresh all spotlight data.