The Chosen Size Is Not Valid for the Chosen File System 69850

Restore a bootable USB flash drive to normal on MacOS

If you are trying to format a USB disk on Mac OS Mojave or newer and get the below error.

The chosen size is not valid for the chosen file system.

Go to Terminal and first check the USB device path

$ diskutil list
/dev/disk0 (internal):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme 500.3 GB disk0
1: EFI EFI 314.6 MB disk0s1
2: Apple_APFS Container disk1 500.0 GB disk0s2
/dev/disk1 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme – +500.0 GB disk1
Physical Store disk0s2
1: APFS Volume Macintosh HD 395.2 GB disk1s1
2: APFS Volume Preboot 44.9 MB disk1s2
3: APFS Volume Recovery 512.8 MB disk1s3
4: APFS Volume VM 4.3 GB disk1s4
/dev/disk2 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *8.0 GB disk2
1: 0x17 3.1 GB disk2s1
2: DOS_FAT_12 720.9 KB disk2s2

As you can see the external device is /dev/disk2.

Zero out the disk with a simple command like below.

$ diskutil zeroDisk /dev/disk2
Started erase on disk2
Finished erase on disk2

Now you can select the disk from Disk Utility and change the filesystem to any format of your choice.

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