macbook air "Aboout This Mac" storage indicator incorrect

1. Re-index Macintosh HD.

Spotlight reindexing will take a while to finish.

System Preferences > Spotlight > Privacy

http://support.apple.com/kb/ht2409

You will see a new category “Other” in the Storage Display.

About “Other”:

http://support.apple.com/en-us/HT202867

2. Try OmniDiskSweeper. This will give the storage size details of the items.

https://www.omnigroup.com/more

Select Macintosh HD and click “Sweep Selected Drive” at the bottom.

Delete the files yo don’t want to keep.

Be careful. Delete only the files that can be safely deleted.

3. Discrepancy in calculating space between Finder and Disk Utility

“Finder does not take into account the Backups/ local snapshots,

but disk utility includes them.”

http://pondini.org/TM/30.html

Welcome to the joys of Spotlight - a wonder when it works (or a wonder that it works) I get confused about that. 🙂 The spotlight index seems to become corrupted rather easily - dominic has shown you how to do the reindex which should make it more accurate. In Disk Utility verify the disk (not permissions) and assuming it reports no repairs are necessary you can trust the information it give you. If it reports that repairs are needed reboot holding Command R and once you’ve booted into the Recovery partition you can run Disk Utility and repair the drive.

Open System Preferences and select the Spotlight Tab. Click on the Privacy tab and drag your hard drive icon onto the window. Not just one folder - the entire hard drive. Quit System Preferences. This will delete the spotlight index. Open System Preferences again, select the SpotLight tab, and select your hard drive icon. Click on the minus sign to delete it from the list. Quit System Preference. This should start the computer reindexing. For a while your computer will feel slow and the fans will probably gear up.

Not dumb at all - by default the Mac’s hard drives are hidden from the desktop. Rumor has it that Steve Jobs hated a desktop that had stuff on it. Unlike Jobs, I like having the hard drive icon. In the menubar select Finder > Preferences and select the General tab. At the top you can click checkmarks to show the internal drive, external drives, etc. Click on the first one (hard disks) and your computer’s hard drive will appear in the top right corner.

Or, open a Finder window and scroll through the sidebar to the left until you find Devices. The first item under Devices should be your computer (it’ll have whatever name you gave your computer). Click on your computer and the window will show the Macintosh HD (and probably several other things). Your hard drive is the Macintosh HD.