How to format a Mac USB drive to use in Windows

By default, macOS formats USB storage devices (such as flash drives) with a file format that is not recognized by Windows. In order to use a USB storage device in Windows, it will need to be "formatted" with a file system that both operating systems recognize. NOTE: This process will erase all data on the storage device, so be sure to copy any necessary files to the computer first.

1. Connect your USB storage device to a Mac computer.
2. Open Disk Utility (Applications > Utilities > Disk Utility or do a Spotlight search).
3. Select the device from the list in the External section on the left-hand side.
   
4. Click the "Erase" button.
5. Select "ExFAT" as the format. The scheme can remain as "GUID Partition Map".
   
6. Click "Erase" and follow all remaining prompts to continue. If macOS then prompts to use the storage device as a Time Machine backup, decline.