YouTube Thumbnail Previewer
See exactly how a thumbnail will sit in a desktop search result, a watch-page sidebar and a mobile feed card — at real relative scale — and check it against YouTube's own resolution, file size and format rules before you upload it. The image never leaves your device.
How to check a thumbnail
- Drop in an image. It is read locally — nothing uploads, and there is no engine to download.
- Review the checklist — aspect ratio, resolution, file size and format, each checked against YouTube's own published rules.
- Scroll to how it looks in context to see the image composited into a desktop search row, a sidebar suggestion and a mobile feed card at real relative scale.
- Anything cropped in the mockups is telling you the same thing the aspect ratio check is: the source isn't 16:9.
- Copy summary to paste the full checklist into a ticket, a chat, or a note for later.
Frequently asked questions
Is my thumbnail uploaded anywhere to preview it?
No. The image is read straight from your device and composited into the mockups entirely in your browser. Nothing is uploaded, there is no account, and no copy of the file leaves your machine.
What size and format should a YouTube thumbnail be?
1280 × 720 at 16:9 is the long-standing baseline and still works; YouTube's current recommendation is 3840 × 2160 for large screens. The minimum accepted width is 640px. JPG and PNG are the accepted formats — the full envelope, including the file size limits, is on /specs/youtube-thumbnail-size.
Why does my thumbnail look cropped in the mockups?
Because it isn't 16:9. YouTube's thumbnail slot is a fixed 16:9 box everywhere it appears, so any other shape is centre-cropped to fill it — the same crop the mockups on this page apply. Export at 16:9 to keep control over what gets cut.
Why does the file size check show two different limits?
YouTube enforces a smaller ceiling for uploads from its mobile app than from a desktop browser. A thumbnail under the mobile limit is safe everywhere; one between the two limits will upload fine from a computer but be rejected from the app.
Does passing every check guarantee YouTube will accept it?
It means the image matches every documented rule this page checks — aspect ratio, minimum resolution, file size and format. YouTube can still reject an upload for reasons outside those rules (policy violations, for instance), so this is a pre-flight check, not a guarantee.
Where do I get a source image to test?
A frame pulled straight from your own video is usually the best source — it's already correctly exposed and graded. The Frame Grabber tool extracts a full-resolution still from any video frame, which you can then check here.