Format a Bootable USB drive to full capacity using a Mac

Hi,

It is possible that 48GB capacity out of 64GB is used for Windows partition which could not read with Mac.

Try to reformat with Windows PC as NTFS, then reformat with DiskUtility of macOS as APFS or Extended (Journaled).

Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drives appear on the left pane of Disk Utility. Select the whole physical drive to erase.

Sometimes macOS & Disk Utility are just not able to handle some drives which have utilized other operating systems....especially when "burned" to a drive from an .iso or .img raw image file. In those cases you may need to write zereos to the very beginning of the drive in order to destroy the partition table. You can do this by using the Terminal command line. First you need to get the drive identifier for the physical drive you want to erase....it will be in the format like "diskX"....for example it may be "disk4".

Here is the command template needed to erase the beginning of the drive with identifier "diskX". Replace "diskX" with the correct drive identifier for the drive you want erased.

sudo  dd  if=/dev/zero  of=/dev/diskX  bs=100m  count=10

This command will prompt you for your admin password. Nothing will appear on the screen as you type the password, so you will need to press the "Return" key to submit the password. For example, if the identifier for the drive you want to erase is "disk4", then here is the command you would use:

sudo  dd  if=/dev/zero  of=/dev/disk4  bs=100m  count=10

After writing zeroes to the beginning of the drive, you should then be able to use Disk Utility to erase the drive normally (make sure to select the whole physical drive).

Or as @kaz-k suggested, you can use Windows to delete all existing partitions and partition & format it before connecting to your Mac where you can use Disk Utility to erase the whole physical drive.