The short answer
YouTube recommends a thumbnail of 1280 × 720 pixels, using a 16:9 aspect ratio — the same shape as the video player itself. That's the size to design at from the start, since it's also what most thumbnail makers set as their default canvas.
At 1280×720 your thumbnail stays sharp in the full watch-page player, in search results, in Suggested videos, and in the small mobile feed — where most viewers actually see it first.
Minimum and maximum limits
YouTube will accept an image as small as 640 × 360 pixels, but anything below the recommended size gets upscaled and softened by YouTube's own player — so treat 640×360 as a hard floor, not a target.
On the other end, uploads are capped at a 2MB file size. A well-compressed JPEG at 1280×720 usually lands well under that limit; if you're exporting a PNG with a lot of detail, check the file size before you upload.
Supported file formats
YouTube accepts JPG, PNG, non-animated GIF, and BMP. JPG is the safest default — it compresses photographic images well and rarely runs into the 2MB ceiling. Reach for PNG only when you need transparency mid-edit; flatten and export as JPG for the final upload.
Why 16:9 matters
Thumbnails that aren't 16:9 get automatically cropped by YouTube to fit the player and grid tiles — usually from the sides or top and bottom, depending on the source shape. That crop happens after upload, so what you designed and what viewers see can end up different. Starting your canvas at 1280×720 avoids the guesswork entirely.
Common sizing mistakes
The most common issue is designing on a square or vertical canvas — a habit carried over from Instagram or TikTok — and then having YouTube crop out a subject's face or headline text. A close second is exporting a huge, uncompressed PNG that either fails the 2MB check or gets silently recompressed and loses sharpness. Both are avoided by starting at 1280×720 and exporting as a compressed JPG.
Quick checklist
Before you upload, confirm: canvas is 1280×720 (or at least 640×360), aspect ratio is exactly 16:9, file is JPG or PNG, and the file size is under 2MB. Our Thumbnail Size Checker will verify all four in your browser before you upload.