YouTube thumbnail size checker

How to use the youtube thumbnail size checker

1. 01Drop in your thumbnail, or choose a file.
2. 02Read each check: the required ones stop an upload if they fail, the recommended ones don't.
3. 03Fix anything marked required, then check again.

YouTube thumbnail dimensions and file limit

YouTube's own thumbnail requirements page states a recommended resolution of 3840 x 2160 pixels for a video thumbnail, with a minimum width of 640 pixels. A Shorts thumbnail uses the same numbers turned on their side: 2160 x 3840 recommended, with a minimum height of 640 pixels. The page names JPG or PNG as the image formats to upload in. Uploading a custom thumbnail at all, in any format, also requires a verified YouTube account: an unverified account doesn't get the option. (Verified against support.google.com/youtube/answer/72431, 22 September 2026.)

File size depends on where you upload from. On the YouTube mobile app the limit is 2 MB for a video thumbnail, or 10 MB for a podcast thumbnail. On desktop the limit is more generous: 50 MB for a video, Shorts or podcast thumbnail alike. A thumbnail under 50 MB will upload from a computer even if it is too large for the mobile app, which is why this checker treats the desktop limit as required and the mobile limit as a recommendation. (Verified against the same page and date.)

One more detail worth knowing: on a vertical video, YouTube replaces a 16:9 custom thumbnail with an auto-generated 4:5 thumbnail on the home, explore and subscriptions pages. (Verified against the same page and date.)

Why thumbnails get rejected

This checker treats three things as required: a format other than JPG or PNG (the formats YouTube's page names), a width under the minimum, and a file over the desktop size limit. YouTube doesn't publish a complete list of everything its upload form validates, so this isn't a guarantee that nothing else can go wrong, but these three are the closest matches to what the page states as rules rather than recommendations, and any one of them failing is worth fixing before you upload.

Everything else, an aspect ratio away from 16:9, a resolution short of the 3840 x 2160 recommendation, or a file that clears the desktop limit but not the stricter 2 MB mobile one, is accepted by YouTube but flagged here as a recommendation. A thumbnail that clears every recommended check is the one least likely to look stretched, need re-uploading from a computer because it was too large to upload from the mobile app, or need a second export before it looks right in every placement.

Designing for small screens

A thumbnail is judged small long before anyone sees it at full size: in a mobile feed, a sidebar suggestion, or search results on a phone, it renders at a few hundred pixels wide, not the 3840 x 2160 it was uploaded at. Fine detail, a small face in a wide shot, thin text, disappears at that size well before it disappears on a desktop monitor.

Large, legible text and a subject that reads clearly at a glance survive that shrink better than a busy composition does. Previewing the finished thumbnail at roughly the size it will actually be shown, rather than only checking it full-screen in an editor, catches the kind of problem that only shows up once the video is live.

How the numbers are worked out

Every rule above is read directly from YouTube's own thumbnail requirements page (support.google.com/youtube/answer/72431), checked on 22 September 2026. Minimum width and the desktop file size limit are hard figures that page states outright, so this checker treats both as required. Format is treated as required too, but conservatively: the page names JPG or PNG with "such as", not a closed list, so a file in another format is flagged to be fixed rather than guaranteed to fail. The recommended checks use the figures the page states as recommendations: aspect ratio, the recommended resolution, and the stricter mobile file size limit.

Questions about the youtube thumbnail size checker

What size is a YouTube thumbnail?

YouTube's own page recommends 3840 x 2160 pixels for a video thumbnail, 16:9, with a minimum width of 640 pixels. A Shorts thumbnail uses the same numbers the other way round: 2160 x 3840 recommended, with a minimum height of 640 pixels.

What is the maximum file size for a YouTube thumbnail?

It depends on where you upload from. YouTube states 2 MB for a video thumbnail uploaded from the mobile app, and 50 MB for a video, Shorts or podcast thumbnail uploaded from desktop. A file under 50 MB but over 2 MB will upload from a computer but not from the app.

Can I use a WebP thumbnail?

YouTube's requirements page names JPG or PNG, not WebP, as the formats to upload in. This checker treats that as a required fix to be safe, since WebP isn't one of the named formats: convert to JPG or PNG first if you're not sure.

Why is my thumbnail blurry after upload?

Usually because the source image was smaller than the space YouTube displays it in. A thumbnail uploaded well under the recommended 3840 x 2160 gets scaled up in larger placements, which softens fine detail and text. Uploading at or near the recommended resolution, rather than the bare 640-pixel minimum, avoids that.

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Updated 22 September 2026 · All free tools