Current file guide
YouTube thumbnail size, format, and upload limits
YouTube currently recommends a 3840 × 2160 image in a 16:9 aspect ratio, with a minimum width of 640 pixels. File limits differ between desktop and mobile uploads. Check the export file before you spend live traffic on an A/B test.
Run a free preflight
Use the current source, not an old template
YouTube's recommendation is now 3840 × 2160
Older articles often repeat 1280 × 720 and a universal 2 MB cap. YouTube's current help page gives a larger recommended resolution and separates file limits by upload device.
Long-form video thumbnail
Use a 16:9 image. YouTube recommends 3840 × 2160 and says the width must be at least 640 pixels.
Formats YouTube lists
The current help page names JPG, GIF, and PNG. Check the page again before exporting because the list and limits can change.
Upload size depends on the device
For video thumbnails, YouTube currently lists 50 MB on desktop and 2 MB on mobile. Podcast thumbnail limits are different.
Shorts use a different workflow
You cannot upload a custom thumbnail for Shorts in the same way as a long-form video. YouTube lets you select a frame for specific surfaces instead.
Before a native A/B test
Keep every finalist at 1280 × 720 or higher
YouTube says that if any experiment thumbnail is below 720p, every thumbnail in that test is downscaled to 854 × 480. One small file can therefore lower the resolution of the whole set.
- 01
Export every finalist from the same 16:9 canvas.
- 02
Keep every option at or above 1280 × 720. Use 3840 × 2160 when your source artwork supports it.
- 03
Check the final JPG, GIF, or PNG file rather than the editable design document.
- 04
Upload all options through the same device workflow so the applicable file limit is clear.
Two separate file contracts
A file that works here is not automatically ready for YouTube
Thumbnail AB Test uses its own limits to keep a six-image browser comparison bounded. Those limits describe this preflight tool. They do not replace YouTube's upload rules.
| YouTube final upload | Thumbnail AB Test preflight | |
|---|---|---|
| Purpose | Publish or run a native audience test | Compare creative files before publishing |
| Resolution | 3840 × 2160 recommended; 640 px minimum width | Up to 20 megapixels per image |
| Listed formats | JPG, GIF, PNG | Static JPG, PNG, WebP |
| File size | Video thumbnail: 50 MB desktop, 2 MB mobile | 16 MiB per image; 48 MiB per comparison |
| Animation | Follow YouTube's current upload guidance | Animated files are rejected |
If you compare a WebP file here, export the finalist in a format YouTube currently lists before upload. Keep the original design file so you can make that export without enlarging a small raster image.
YouTube custom thumbnail guidanceFinal export check
Five checks before upload
Open the exported file, not just the design canvas. A filename ending in .png does not prove the file has the right dimensions or byte size.
- The image uses a 16:9 canvas for a long-form video.
- The exported pixels match the size you intended.
- Every native A/B test option is at least 1280 × 720.
- The file format and byte size fit the device you will use to upload.
- The title and thumbnail still describe what the video delivers.
Official YouTube references
YouTube can change dimensions, formats, limits, and eligibility. This page uses a 90-day source review window.
Checked .
- YouTube custom thumbnail guidanceCurrent resolution, aspect ratio, listed formats, device limits, and Shorts notes
- YouTube A/B test titles and thumbnailsCurrent three-option workflow and experiment downscaling rule
File questions
YouTube thumbnail size and format answers
What size should a YouTube thumbnail be?
YouTube currently recommends 3840 × 2160 pixels in a 16:9 aspect ratio, with a minimum width of 640 pixels. Use the largest clean export your source artwork supports rather than enlarging a small image after export.
Can I still use 1280 × 720?
YouTube's current custom thumbnail page recommends 3840 × 2160 and allows a minimum width of 640 pixels. Its A/B testing page treats 1280 × 720 as the 720p threshold: if any test thumbnail is smaller, YouTube says it downscales every option to 854 × 480.
Does every YouTube thumbnail have a 2 MB limit?
No. YouTube currently lists 2 MB for video thumbnails uploaded on mobile and 50 MB on desktop. Podcast thumbnail limits differ, so check the official page for the device and content type you will use.
Can I upload WebP to YouTube?
Thumbnail AB Test accepts static WebP for browser-based preflight. YouTube's current custom thumbnail guidance lists JPG, GIF, and PNG. Export the final candidate in a format YouTube lists instead of assuming this tool's intake formats are YouTube upload formats.
Can I upload a custom thumbnail for YouTube Shorts?
YouTube says you cannot upload a custom thumbnail for Shorts in the same way as a long-form video. You can select a frame for search results, hashtag and audio pages, and the channel page, and YouTube says that selection cannot be changed after upload.
Why should every A/B test thumbnail use the same resolution?
YouTube says that if any experiment thumbnail is below 720p, all experiment thumbnails are downscaled to 854 × 480. Keeping every option at 1280 × 720 or higher avoids that set-wide downscaling rule.
Continue the workflow
Check the file, then compare the idea
Use the file guide for export rules, the pre-publish guide for the full testing sequence, or the methodology page for the score's limits.
Your files are ready. Compare the complete packages.
Add each exported thumbnail with its title, inspect the weakest signal, and keep live audience traffic for the finalists.