Fix the YouTube “file too large” error
YouTube rejects thumbnails over 2 MB. This tool resizes to 1280x720 and then compresses until the file actually fits, rather than leaving you to guess at a quality slider.
JPG, PNG or WebP
Exports at 3840x2160, 1280x720 (under 2 MB), or Shorts 9:16.
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Why exports from design tools fail
Canva, Figma and Photoshop all default to high-resolution PNG, which is exactly the wrong combination for this limit: lossless compression on a large canvas produces enormous files. Re-encoding as JPG at 1280x720 routinely takes a 5 MB export under 200 KB with no visible difference at the size a thumbnail is actually viewed.
What the 2 MB limit really covers
It applies to the custom thumbnail image itself, not the video, and it is enforced at upload with an unhelpful error that does not say which part was wrong. Dimensions are not usually the problem — a 4K thumbnail is allowed if it fits in 2 MB. It is nearly always the file size, and nearly always a PNG.
The blur fit and when to use it
When your image is not 16:9, something has to fill the gap. The blur fit puts an enlarged, softened copy of the image behind it, which reads as deliberate rather than as an accident, and keeps the whole picture visible. It is the right choice for a vertical photo or a screenshot you cannot afford to crop.
Frequently asked questions
What format should I use?
JPG for anything photographic, which is most thumbnails, and it is what keeps you under the limit. PNG only for graphics with sharp text or transparency, and watch the size closely if you do.
Will compressing make it look worse?
Not noticeably at thumbnail size. Compression artefacts show up under close inspection at full resolution, and a thumbnail is displayed a few hundred pixels wide, where they are invisible.
YouTube still rejects it. What else could be wrong?
Check that your account is verified, since custom thumbnails need it. Otherwise confirm the file is JPG, PNG, GIF or BMP — an unusual format or a mislabelled extension will be refused whatever its size.