If you are trying to create new a bootable drive in Rufus but keep getting the "Undetermined error while formatting,” error it means the process failed during the formatting stage, before it could write the bootable image to the USB drive. If this step fails, Rufus stops and the bootable USB cannot be created, so follow along as this guide walks you through all of the known solution that will solve this problem.

Takeaways:

  1. What keeps causing error “Undetermined Error While Formatting” in Rufus when creating a Windows ISO?
  2. Learn how to fix “Undetermined Error While Formatting” error in Rufus when creating bootable media.

How to Fix “Undetermined Error While Formatting” in Rufus

This error is rarely caused by Rufus itself. In most cases, it's because of a hardware or system level issue. The most common cause usually failing or low quality USB flash drives, unstable USB ports or hubs, a write protected state, file system or partition corruption, or background software that is locking the drive.

Replug the USB drive and change ports

Connection problems are a frequent cause of low level formatting failures. Start by ruling out port and cable issues.

  • Unplug the USB drive.
  • Wait about 10 seconds.
  • Plug it directly into the computer, not through a hub or dock.
  • Try a different USB port.
  • On desktop PCs, use a rear motherboard port.
  • On laptops, use a built in port and avoid pass through hubs.
  • If available, test both USB 3.x and USB 2.0 ports.
  • If the error continues, test with a different USB drive.

Note: If the same USB drive fails on multiple computers, or shows symptoms like zero capacity, “No media,” or remaining in RAW state even after cleaning, it is very likely dead.

Do a clean Windows format, then force a full format in Rufus

Pre formatting the drive in Windows can clear basic file system corruption before Rufus takes over. This step is only meant to reset the drive, not to choose the final file system.

  • Insert the USB drive.
  • Press Win + E to open File Explorer.
  • Right click the USB drive and select Format.
  • Choose FAT32 if available and click Start.

How to Fix Undetermined Error While Formatting in Rufus

Note: FAT32 is widely compatible and works well as a temporary clean slate. If FAT32 is not available, continue with the offered option.

Now, configure Rufus to perform a more thorough format.

  • Run Rufus as Administrator.
  • Select the correct USB drive under Device.
  • Choose your bootable ISO under Boot selection.
  • Open advanced format options.
  • Disable Quick format.
  • Click Start and allow the process to finish without unplugging the drive.

Disabling Quick format forces Rufus to do a full format pass. This takes longer but helps detect bad blocks and avoids fast format related failures. If this step fails again, the USB drive is very likely unreliable.

Windows Options

When using a Windows ISO, Rufus may display additional options such as disabling automatic BitLocker device encryption. These settings only affect how Windows behaves after installation.

  • They do not affect USB formatting.
  • They do not cause “Undetermined error while formatting.”
  • You can usually leave them at their default values while troubleshooting.

If your issue is a formatting failure, focus on hardware, ports, and formatting steps rather than these options.