Sizes
| What | Size | Ratio | Note |
|---|---|---|---|
| Video thumbnail | 3840 x 2160 | 16:9 | minimum width 640 pixels |
| Shorts thumbnail | 2160 x 3840 | 9:16 | minimum height 640 pixels |
| Older guides | 1280 x 720 | 16:9 | YouTube's own page says 3840 x 2160 |
| Podcast playlist | 1:1 | 1:1 instead of 16:9 | |
| Vertical video, 16:9 thumb | 4:5 | replaced by an auto-generated 4:5 thumbnail | |
| File size, mobile | 2 MB | 2 MB for video thumbnails or 10 MB for podcasts | |
| File size, desktop | 50MB | 50MB for video, Shorts, and podcast thumbnails |
Sizes from Add custom thumbnails on YouTube - Computer, read 21 October 2026.
How to use the tool
- Add a photo: drop a JPG, PNG, WebP, AVIF, HEIC or JFIF, or choose one from your device.
- Pick a size. Drag and zoom the crop box until the part you want sits inside it.
- Download a JPG (the default) or a PNG, drawn at the exact width and height you picked. Nothing is uploaded.
What the size means
YouTube's page "Add custom thumbnails on YouTube - Computer", read 21 October 2026, says 3840 x 2160 for videos and 2160 x 3840 for Shorts, with a 640-pixel minimum. Older guides say 1280 x 720. YouTube's own page says 3840 x 2160. Upload JPG or PNG. Mobile: 2 MB; desktop: 50MB. The default JPG is kept under 2 MB by stepping quality down until it fits. Videos 16:9; Shorts 9:16; podcast playlists 1:1. A 16:9 thumb on a vertical video is replaced by an auto-generated 4:5 thumbnail on home, explore, and subscription pages.
Questions
Is it private?
Yes. The crop runs in your browser. No file is sent to creavio or anyone else, and nothing is stored after you close the tab. The HEIC decoder downloads once, the first time you add a HEIC photo.
Which formats can I use?
JPG, JPEG, JFIF, PNG, WebP, AVIF and HEIC. SVG files are not accepted. The page uses the same decoders as the converters, including the HEIC decoder.
Why not 1280 x 720?
Older guides say 1280 x 720. YouTube's own page, read 21 October 2026, says 3840 x 2160 for videos and 2160 x 3840 for Shorts.
Will the JPG stay under 2 MB?
The default JPG is encoded under 2 MB, the mobile limit. Desktop allows 50MB. The page shows the final size. PNG is offered too.
Which browsers does it work in?
Current versions of Chrome and Safari. It uses only features built into the browser, so there is nothing to install.
HEIC decoding uses heic-to and libheif, free software licensed under the GNU LGPL 3.0. They are included unmodified as a separate file, loaded only when you add a HEIC photo. The source code is at the links above.