Formatting an External Drive for Use on Mac and Windows

Warning

This process will erase any data on the drive! Step 1 is very important!

Step-by-Step

Macintosh

1. Plug in external drive. Copy all existing data on the USB drive to a folder on your Desktop.
2. Open Finder, go to Applications, Utilities, and open Disk Utility.
3. On the left side of Disk Utility, select the USB drive you want to reformat.
   • Make sure to click the top level drive name, and not the individual partitions (the sub-items).
4. On the top of the right side of Disk Utility, click Partition.
5. On the drop down for Partition Layout, select 1 Partition.*
6. For Format, select MS-DOS (FAT).
7. Choose a name for the drive and enter it into the Name field.
8. The size should reflect the total capacity of the drive. There will be a little less than the advertised size (eg., a 16GB drive may only show 15.2GB).
9. Verify that you have backed up all the existing contents of the drive to a separate location (Step 1).
10. Click Apply, and wait for Disk Utility to finish. You can see the progress on the bottom right of the window.
11. Your drive will now be readable by both Mac and Windows machines.

*You can create a multiple partition drive, which has some benefits as well as drawbacks. If you choose more than 1 partition in step 6, you will see multiple white boxes on the left. You can modify each partition by clicking on the box and using steps 7-8, and resize the partition by dragging the line between the boxes up and down. 

Windows

1. Plug in external drive. Copy all existing data on the USB drive to a folder on your Desktop.
2. Open File Explorer window.
   • The easiest way is to hit Windows Key + E on your keyboard. The Windows key is the key between Ctrl and Alt on most keyboards.
   • You can also click the Start button and type File Explorer and hit enter.
3. Right click the drive you have inserted and click Format...
   • Make sure you right click the correct drive, as the next steps will be wiping the selected drive.
4. On the File system dropdown, select either FAT or exFAT.
5. You can give the drive a name by filling in the Volume label field.
6. Leave the Quick format box checked for a faster format, or uncheck to also erase all the data on the drive. Unchecking this box is more secure if there is sensitive data on the drive.
7. Click Start to erase the selected drive and make it compatible with both Mac and Windows systems.