A THM file is a thumbnail image that Windows or another program created automatically to show you a preview of a photo or video

When you take a photo with a digital camera, phone, or camcorder, your device often creates two files at once: the actual image or video, and a much smaller THM file alongside it. THM stands for thumbnail. The thumbnail is a tiny preview picture — usually 120 by 90 pixels or smaller — that lets your computer display a quick preview without having to load the full-size file, which might be several megabytes.

You will most often see THM files if you have backed up photos and videos from a camera or phone to your computer. They sit in the same folder as the original files and have the same name, with .THM added to the end. For example, if your photo is named IMG_2024.JPG, the thumbnail file will be IMG_2024.THM. Your computer created these files automatically — you did not make them yourself.

THM files are harmless and take up almost no space. A single THM file is usually between 5 and 50 kilobytes, while the photo or video it represents might be 2 to 10 megabytes. You can delete them without losing the original image, but there is usually no reason to, since they use so little storage.

Key Takeaways

  • THM files are thumbnail previews that cameras and phones create automatically alongside photos and videos.
  • You will see them most often when you back up files from a camera or phone to your computer, sitting in the same folder as the originals.
  • Deleting a THM file does not delete the photo or video it represents, because they are separate files.
  • THM files use almost no storage space — usually 5 to 50 kilobytes each — so there is no practical reason to remove them unless you are organizing a backup.

Where THM files come from

Most digital cameras, smartphones, and camcorders create thumbnail files automatically as they record. The device stores the full-resolution image or video on its memory card, and at the same time writes a tiny preview version to speed up browsing. When you connect the camera or phone to your computer and copy the files over, both the original and the thumbnail come along.

Some backup software and file management programs also create THM files if they do not find them already present. This happens most often when you are organizing old photos that were taken on devices that did not create thumbnails, or when you are consolidating files from multiple sources. The software generates the thumbnail to help you browse the collection faster.

You might also see THM files if you have used certain video editing software or photo management tools. Programs like Adobe Lightroom or older versions of Windows Photo Gallery sometimes create thumbnail caches to speed up previewing large collections.

Whether you should keep or delete THM files

There is no harm in keeping THM files. They take up negligible space — even if you have 10,000 photos with thumbnails, the THM files together might use only 200 to 500 megabytes, while the actual photos would use 20 to 100 gigabytes. Deleting them saves almost nothing.

You might choose to delete THM files if you are trying to organize a backup and want to keep only the original images and videos. Some people prefer a cleaner folder structure with no extra files. If you delete them, your computer can always generate new thumbnails the next time you browse the folder, so nothing is lost.

If you are backing up files to cloud storage like Google Drive or OneDrive, you may want to exclude THM files from the upload to save bandwidth and storage quota. Most backup software lets you choose which file types to include. Check your backup settings to see if you can filter out .THM files before the transfer starts.

How to identify and manage THM files on your computer

To see THM files on your computer, open the folder where your photos are stored and look for files ending in .THM. On Windows, you can show file extensions by opening File Explorer, clicking the View tab, and checking the box next to "File name extensions." On a Mac, open Finder, go to Preferences, and check "Show all filename extensions" under the Advanced tab.

If you want to delete THM files, select them and press Delete, or right-click and choose Delete. You can select multiple THM files at once by holding Ctrl (Windows) or Command (Mac) and clicking each one. If you want to delete all THM files in a folder at once, you can use the search function: search for *.THM and the system will show only thumbnail files, which you can then select and delete together.

Some file management software can filter out THM files automatically. If you are using a photo organization tool like Lightroom or Photos, check the settings to see whether it can hide thumbnail files from your main library view. This keeps your collection cleaner without actually deleting the files.

THM files from different devices

Different cameras and phones create THM files with slightly different formats, but they all work the same way. Canon cameras create THM files alongside their CRW or CR2 raw image files. Sony cameras do the same with their ARW files. GoPro cameras create THM files for every video. Older phones and some Android devices create THM files in DCIM folders when you back them up.

The THM file format is not standardized across all devices, which means a THM file from a Canon camera might not open in the same way as one from a GoPro. However, you do not need to open them — they are meant to be read by your computer's file browser or by photo software, not by you directly. If you ever need to see the thumbnail, your computer will display it automatically in folder previews.

Frequently Asked Questions

Can I open a THM file and see what it looks like?

Yes, but there is usually no reason to. Most image viewers will open a THM file if you double-click it, and you will see a small preview image. However, the image is so tiny that it is not useful to look at. If you want to see the photo or video, open the original file instead — it will be in the same folder with the same name but a different extension, like .JPG or .MP4.

Will deleting THM files affect my photos or videos?

No. THM files are separate from the original image or video. Deleting a THM file removes only the thumbnail preview, not the photo itself. Your original files remain untouched and fully intact.

Why does my backup have so many THM files?

Your camera or phone created one THM file for every photo or video on its memory card. When you backed up the files to your computer, both the originals and the thumbnails came along. This is normal and expected.

Should I delete THM files before uploading to cloud storage?

It depends on your storage quota and internet speed. THM files use very little space, so deleting them saves only a small amount. However, if you are uploading thousands of files on a slow connection, excluding THM files from the upload can speed things up slightly. Check your backup software settings to see if you can filter them out.

What if I see THM files but no matching photos?

This usually means the original photo or video file was deleted or moved to a different folder, but the thumbnail was left behind. You can safely delete the orphaned THM file. If you want to recover the original file, you may need to check your Recycle Bin or use file recovery software, but the THM file itself cannot help you recover it.