Win32 Disk Imager is a small, free Windows program for writing a raw disk image, an .img file, to an SD card or USB drive, and for reading a card back into an .img file. It copies the image sector by sector, so the destination ends up as an exact copy of the original disk layout, including its partitions and boot code.
This guide is for you if you have already downloaded an .img file and you need to get it onto a card or drive that will boot or run in another device. You do not need to understand disk geometry or command-line tools to follow it, but you do need to be careful about one thing above all else: the drive letter you select will be completely overwritten.
Win32 Disk Imager is Windows-only software released under the GPLv2 licence. The current version is v1.0.0, released on 2017-03-08. There is no Mac or Linux version of this program. The installer is about 12.6 MB and the portable zip is about 17.0 MB. The maintainer returned in November 2024, and no new release has appeared since, so you should not describe the project as permanently discontinued, but you should also not expect a new version soon.
Before you start
- Win32 Disk Imager Write overwrites the ENTIRE destination drive. Everything on that drive will be lost, including files in partitions you cannot see in File Explorer.
- Double-check the drive letter in File Explorer and in Win32 Disk Imager before every write. If two removable drives are plugged in, unplug the one you do not want to overwrite.
- Run Win32 Disk Imager as administrator, or Windows may block access to the drive. If you see an access error, closing other programs that use the drive and running as administrator usually fixes it.
- Use a card reader you trust and a card with enough capacity. The destination must be at least as large as the image, and a card that is a few megabytes smaller than the source card can fail even when both are sold as the same size.
- Download the .img file from a source you trust, and keep a copy of it until the flashed card has been tested in its target device.
It helps to prepare the destination before you open the program. Insert the card, wait for Windows to recognise it, and open File Explorer to confirm its letter and its size. If Windows offers to format the card, choose Cancel. You do not need to format first, because writing the image replaces the partition table and all existing partitions anyway. Formatting first only wastes time and can hide a drive-letter mistake.
Step by step
1. Download and install Win32 Disk Imager
Get the program from the download page, install it, and launch it as administrator by right-clicking its shortcut and choosing Run as administrator. The installer MD5 be92e76baabc97b3f093ff734dd3f75b and SHA-256 a51c9fc75c9caa44df03502838f229a70d484963f54675c241799093a59d8874 may be called verified, and you can compare them against your downloaded installer if you want an extra check before installing.
2. Select the image file
Click the folder icon next to the Image File field and browse to your .img file. If the file picker does not show your file, change the filter to show all files, and check the extension carefully. Win32 Disk Imager writes raw images, so the file should end in .img or, in some cases, .img.gz that you have already decompressed. Do not rename an ISO file to .img and expect it to work, because the contents are different even if the extension looks similar.
3. Select the correct device
Use the Device drop-down to choose the drive letter of your SD card or USB drive. Compare this letter with the one you saw in File Explorer, and check the size if anything looks uncertain. If the letter you expect is missing, close and reopen the program, reseat the card, or try another reader. Never guess at this step, because the next step erases the drive you selected.
4. Press Write and confirm
Click Write, read the confirmation dialog, and confirm only if the drive letter is the one you intend to erase. The progress bar shows the write advancing, and the speed depends on your card, your reader, and whether you are using USB 2 or USB 3. Do not remove the card, close the program, or put the computer to sleep while the write is running, because an interrupted write leaves a half-written card that will not boot.
5. Wait for the success message
Wait until Win32 Disk Imager reports that the write was successful, then use Safely Remove Hardware before taking the card out. If the program offers to verify, or if you want extra confidence, run a verify pass afterwards, which is covered in the Verify Only guide. Ejecting the card cleanly matters more than it seems, because Windows may still be flushing cached writes when the progress bar finishes.
6. Test the card in its target device
Put the card into the device it was made for, such as a Raspberry Pi, and power it on. A first boot can take longer than later boots, especially if the system expands its filesystem or generates keys on first start. If the device shows nothing at all, work through the boot checklist guide before you assume the image was bad, because power supplies, HDMI detection, and card seating cause many apparent failures.
Frequently asked questions
Does writing an image erase everything on the card?
Yes. Write overwrites the entire destination drive, including every partition and every file on it. Move anything you need off the card before you press Write, and double-check the drive letter.
Can Win32 Disk Imager make a bootable Windows USB from an ISO?
No. It does not parse ISO filesystems, so it cannot build a Windows installer USB from a Windows ISO. Use Rufus for that job, and reserve Win32 Disk Imager for raw .img files.
Do I need to format the card before writing?
No. Writing the image replaces the partition table and all partitions, so a prior format is unnecessary. If Windows asks to format the card, choose Cancel and write the image instead.
For the full set of guides, see the Tutorials hub, and get the program from the download page. Related guides include: how to back up sd card to img, flash raspberry pi os win32 disk imager, win32 disk imager verify only — each one covers one job in the same plain style as this guide.