Create a bootable USB flash drive using large capacity drives

USB flash drives above 32GB will often fail to boot correctly on some systems even after being made bootable with tools like Rufus or the Windows Media Creation Tool, because the boot partition itself needs to stay within a size range firmware expects. Repartitioning the drive with DiskPart resolves it.

Do You Actually Need to Do This? (Updated for 2026)

Usually not, if you’re using Rufus itself to build the media. Rufus sizes the boot partition to match the actual content it’s writing rather than spanning the entire disk, so the classic “oversized FAT32/exFAT partition confuses older firmware” problem doesn’t normally arise when Rufus (or the Windows Media Creation Tool) does the formatting and copying for you — even on a drive well over 32GB. Manual DiskPart partition-shrinking is still genuinely useful in one specific scenario: when you’re building the media yourself by hand — formatting the whole drive as one large partition and then xcopy/robocopy-ing the extracted ISO contents onto it — rather than letting Rufus or the MCT manage the disk layout. If that’s your workflow, or you’re troubleshooting a drive that still won’t boot despite using Rufus, the steps below still apply.

Steps

1. Plug in the USB drive and open an elevated Command Prompt.
2. Run diskpart to enter the DiskPart console.

list disk
select disk #
clean
create partition primary
select partition 1
active
shrink desired=32768 minimum=32768
format fs=ntfs quick
assign

Replace # with the correct disk number for your USB drive — double-check this against the size shown in list disk before running clean, since that command wipes the selected disk entirely. This creates a 32GB active partition on the drive regardless of its total capacity, which keeps it within the size boot firmware expects. Once formatted, copy your Windows installer files across as normal (via xcopy/robocopy, or by mounting the ISO and dragging the contents over) and the drive will boot correctly. One further gotcha worth checking if a drive still refuses to boot after this: confirm the target system’s firmware boot mode (UEFI vs. Legacy/CSM) matches how you formatted the partition — an NTFS-formatted USB won’t boot under pure UEFI without a compatible boot loader, which is one reason tools like Rufus offer a separate “GPT for UEFI” option rather than always formatting as NTFS/MBR.