A THM file stores thumbnail images that Windows creates automatically

A THM file is a small image file that Windows generates to show a preview of photos, videos, or documents in folder views. When you open a folder full of pictures, Windows creates these thumbnail files behind the scenes so it can display the tiny preview images quickly instead of loading the full-size files every time you scroll.

The name "THM" is short for "thumbnail." You will usually find these files in a hidden folder called Thumbs.db on Windows, or in a .thumbnails folder on Mac and Linux systems. Most of the time you never see them because your operating system hides them by default — they are meant to work in the background.

THM files are not the same as the original image or video. They are compressed copies, much smaller and lower quality, created only to make your folder browsing faster. If you delete a THM file, Windows straightforward creates a new one the next time you open that folder.

Key Takeaways

  • THM files are thumbnail previews that Windows creates automatically to speed up folder browsing.
  • You typically will not see THM files because they are stored in hidden system folders like Thumbs.db.
  • Deleting THM files is safe and will not harm your photos or videos — Windows will recreate them automatically.
  • Some cameras and phones also create THM files alongside video recordings to show a preview image.

Where THM files live on your computer

On Windows, the main THM file storage is a hidden database file called Thumbs.db. This file sits inside the folder you are viewing and holds thumbnail previews for all the images in that location. Because it is hidden by default, you will not see it when you open a folder — Windows keeps it out of sight to reduce clutter.

To see hidden files on Windows 10 or 11, open File Explorer, click the View tab at the top, then check the box next to Hidden items. After that, Thumbs.db files will appear in your folders. On Mac and Linux, thumbnails are stored in a folder called .thumbnails inside your home directory, which is also hidden by default.

Some digital cameras and smartphones create THM files too, but they work differently. When you record a video on a camera, it often saves a small THM file alongside the video file to show a still image preview. These camera-generated THM files are not hidden — they appear right next to your video files.

Why your computer creates THM files automatically

Loading a full-size photo takes time. If you have a folder with 200 high-resolution images, your computer would have to read and decode each one just to show you a preview. That would make scrolling through folders painfully slow. THM files solve this by storing pre-made, compressed previews that load when ready.

When you first open a folder full of images, Windows reads each photo, shrinks it down to thumbnail size, and saves that smaller version in Thumbs.db. The next time you open that same folder, Windows loads the thumbnails from the database instead of processing the full images again. This is why folder browsing feels snappy even with thousands of photos.

The trade-off is that THM files take up disk space, though usually not much — a folder with 100 photos might generate a Thumbs.db file of just a few megabytes. For most people, the speed gain is worth the small storage cost.

When you might want to delete THM files

Deleting THM files is completely safe. They are not part of your actual photos or videos — they are just cached previews. If you delete Thumbs.db or the .thumbnails folder, your images and videos remain untouched. Windows will straightforward recreate the thumbnail files the next time you browse those folders.

Some people delete THM files to free up disk space, though the amount recovered is usually small. Others delete them if thumbnails are displaying incorrectly — for example, if a folder shows the wrong preview image for a photo. Deleting and letting Windows recreate the cache often fixes display glitches.

You might also delete THM files if you are concerned about privacy. Thumbnail caches can sometimes retain previews of files you have deleted, so clearing them removes that trace. However, this is a minor privacy measure — it does not affect your actual files or browsing history.

THM files from cameras and phones

Digital cameras, action cameras, and some smartphones create THM files as part of their normal recording process. When you shoot a video on a GoPro, DJI drone, or similar device, the camera saves both the video file and a separate THM file containing a still image from the beginning of the video. This lets you see what the video is about without having to play it.

These camera-generated THM files are not hidden — they appear in your file list right alongside the video. If you copy videos from a camera to your computer, the THM files come along too. You can delete them without affecting the video, but most people leave them alone since they take up minimal space and can be useful for identifying videos quickly.

Some video editing software recognizes THM files and uses them to display video previews in the timeline. If you delete the THM file, the software will either show a blank preview or generate a new one from the video itself, so nothing breaks.

How THM files differ from other image formats

THM files are not a standard image format like JPG, PNG, or GIF. You cannot open a THM file in most image viewers or edit it in Photoshop. They are system files created for a specific purpose — fast folder browsing — and are meant to stay hidden and automatic.

If you try to open a THM file with an image viewer, you might see a corrupted or partial image, or the program might refuse to open it at all. This is normal. The file is not broken — it is just not designed to be viewed directly. The original photo or video is what you should open instead.

Some THM files from cameras are actually JPEG images with a .thm extension instead of .jpg. These can sometimes be opened in image viewers, but they are still just preview images, not the full-quality original.

Frequently Asked Questions

Is it safe to delete Thumbs.db?

Yes, completely safe. Thumbs.db contains only cached preview images. Your actual photos and videos are stored separately and will not be affected. Windows will recreate Thumbs.db the next time you browse that folder.

Why do I see THM files on my camera's memory card?

Your camera creates THM files alongside video recordings to store a preview image. You can delete them if you want, but they take up very little space. If you keep them, they help you identify videos quickly without playing them.

Can I open a THM file in an image viewer?

Some THM files from cameras are actually JPEG images and can be opened, though they will show only a low-quality preview. Most system-generated THM files from Windows cannot be opened in standard image viewers because they are database entries, not standalone image files.

Do THM files slow down my computer?

No. THM files actually speed up folder browsing by storing previews so Windows does not have to process full-size images. They use minimal disk space and have no noticeable impact on performance.

What happens if I show hidden files and see Thumbs.db?

Thumbs.db is a normal system file. You can leave it alone or delete it — either way is fine. If you delete it, Windows creates a new one automatically. Showing hidden files does not change how your computer works; it just makes invisible files visible.