The thumbnail sizes YouTube stores
For every video YouTube keeps the same picture at fixed sizes on its image server, i.ytimg.com, with a WebP copy of each in a separate folder:
maxresdefault.jpg 1280 × 720 Full HD, 16:9
sddefault.jpg 640 × 480 4:3, black bars
hqdefault.jpg 480 × 360 4:3, black bars
mqdefault.jpg 320 × 180 16:9
default.jpg 120 × 90 4:3, black barsThe 4:3 sizes date from before widescreen video, so a 16:9 thumbnail inside them has black bars above and below. A 480 × 360 thumbnail holds a 480 × 270 picture. For a clean image, use Full HD or the 320 × 180 size, or crop the bars off afterwards.
When Full HD is missing
The 1280 × 720 version only exists when the video was uploaded in HD or the creator set a custom thumbnail of at least that size. Older videos and some Shorts stop at 640 × 480. The page checks which sizes exist and shows the largest first, so you are not left with YouTube’s grey placeholder image.
If you need a bigger image, download the largest size and enlarge it with the image upscaler, which adds detail rather than just stretching the pixels. YouTube itself never stores a 4K thumbnail, whatever other sites claim.
A creator who changes the thumbnail replaces the files at the same addresses, but copies cached by your browser or a CDN can show the old picture for a few hours.
JPG or WebP
WebP files are usually 25 to 35 percent smaller than the JPG at the same size and look the same, which makes them a good choice for a web page. JPG opens everywhere, including older editing software and every phone gallery, so pick it when you are not sure. A few older videos have no WebP copy; those sizes show “Not available in this format”.
Using downloaded thumbnails fairly
A custom thumbnail is the creator’s own artwork and is protected by copyright. Reasonable uses include:
- Studying what makes popular thumbnails work: faces, contrast, text size and colour.
- Saving your own thumbnails when the original file is lost.
- Showing a video in a review, news story or lesson with a credit and a link to it.
Reusing someone else’s thumbnail on your own video can get the video removed and the channel a copyright strike.
Lessons for your own thumbnail
Most people first see a thumbnail at about the size of a matchbox on a phone. Check yours at that size: a face, a single bold object and three or four large words work far better than a busy scene. Keep text and faces out of the bottom-right corner, where YouTube shows the video length. Many channels can now upload up to three versions with Test & Compare in YouTube Studio and let YouTube pick the one that is watched most.