I have a 16GB Kingston USB stick that I once used to try out Chrome OS. Afterwards, plugging it back into a Windows machine, the drive only showed 4GB. The rest of the capacity had vanished, and Windows Explorer showed nothing I could delete.

The cause is that the installation split the stick into several partitions. Windows only shows the first partition it can read, and the rest sit in a format Windows does not understand, so they are hidden entirely.

The built-in Disk Management tool usually cannot delete these partitions. You need diskpart from the command line.

A warning before you start

diskpart works directly at the partition level and there is no confirmation step and no undo. Selecting the wrong disk number wipes that drive completely.

Before you begin, unplug every external drive that is not involved, and at the disk selection step check the size carefully to be certain you have the right stick.

The steps

1. Open Command Prompt as Administrator. Press the Windows key, type cmd, right click and choose Run as administrator.

2. Start diskpart:

diskpart

3. List the disks:

list disk

The output looks like this:

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          476 GB      0 B
  Disk 1    Online           14 GB      0 B

4. Identify the USB stick’s disk number. Look at the Size column: a USB stick is usually much smaller than everything else. In the example above the 16GB stick shows as 14GB (because of how the units convert) and is Disk 1.

This is the most important step. Get it wrong and you wipe a hard drive.

5. Select the disk:

select disk 1

6. List the existing partitions:

list partition

A standard USB 2.0 stick usually has 2 partitions. A USB 3.0 stick that has had an OS installed on it can have many more, sometimes up to 10.

7. Delete them one at a time:

select partition 1
delete partition override

Repeat until list partition shows nothing left. The override parameter is required because Windows refuses to delete system partitions without it.

8. Create a single partition again:

create partition primary

9. Exit:

exit

10. Go to This PC and open the USB drive. Windows will say it needs formatting.

11. Format with the default settings and give the drive a name if you want one.

The faster way: the clean command

Instead of deleting partitions one by one, diskpart has a command that wipes everything in one step:

list disk
select disk 1
clean
create partition primary
format fs=ntfs quick
assign
exit

clean erases the entire partition table on the disk. It is much faster than the manual approach above and correspondingly more dangerous, so the select disk step needs even more care.

A few notes on the file system choice:

  • fs=ntfs for a drive you only use on Windows
  • fs=fat32 if you need it to work with TVs, media players or computers running other operating systems. The limitation is that it cannot store files larger than 4GB
  • fs=exfat is the balanced option: most devices read it and there is no 4GB limit

The quick parameter does a quick format. Leave it off and Windows scans the whole surface, which takes much longer but detects bad sectors.

If clean throws an error

If you see DiskPart has encountered an error: Access is denied, check two things:

  • Is Command Prompt actually running as Administrator?
  • Is an Explorer window or another program holding the USB drive open? Close everything and try again.

If it still fails, run attributes disk clear readonly after select disk, then try clean again.