Home › Blog › YouTube Thumbnail Size: Dimensions, File Limits and the Vertical Video Catch
By Prakash Gohel · Updated 2026-09-03 · Sources are linked inline.
These are the figures YouTube publishes on its own custom thumbnail help page (YouTube Help: Add video thumbnails). Every number below comes from that page.
The most common upload failure is not the dimensions — it is the file size, and specifically the gap between the two limits. Desktop allows 50 MB. Mobile allows 2 MB for a normal video thumbnail. A 3840 × 2160 PNG exported from a design tool routinely lands between 5 and 12 MB, which uploads fine from a laptop and is rejected outright from a phone.
The fix is to export as JPG rather than PNG for photographic thumbnails, and to compress before uploading. Run the file through the Image Compressor — it works entirely in your browser using canvas, so the image never leaves your device. If the dimensions are also wrong, use the Image Resizer first and compress second; doing it in that order avoids compressing detail you are about to throw away anyway.
YouTube states that vertical videos with a 16:9 custom thumbnail get that thumbnail replaced by an auto-generated 4:5 thumbnail on the Home, Explore and subscription pages. In other words, if you upload vertical content and design a standard widescreen thumbnail for it, the image you carefully made may not be the one most people see in those feeds.
If vertical video is a meaningful part of what you publish, plan for the crop: keep faces and text within the central 4:5 region of your 16:9 canvas so the automatic crop cannot destroy the composition.
Your 3840 × 2160 export will most often be displayed at a few hundred pixels wide on a phone. Design at full size, then shrink the preview to roughly 210 pixels wide and look at it again.
If you see "Daily custom thumbnail limit reached", YouTube's guidance is simply to try again in 24 hours. And custom thumbnails are a privilege that can be removed — the policy section of that help page is worth reading once, properly, rather than after a strike.
3840 × 2160 pixels at a 16:9 aspect ratio, with a minimum width of 640 pixels, according to YouTube's official thumbnail help page.
2 MB for video thumbnails uploaded from mobile, 10 MB for podcast thumbnails on mobile, and 50 MB when uploading from desktop.
JPG, GIF and PNG.
YouTube replaces a 16:9 custom thumbnail with an auto-generated 4:5 thumbnail on the Home, Explore and subscription pages for vertical videos. Keep key elements inside the central 4:5 area.
Export as JPG instead of PNG for photographic images, and compress before uploading. A browser-based compressor does this without sending the file anywhere.