YouTube Thumbnail Size: Upload vs Download
Two numbers are often mixed together: the size YouTube currently recommends for a custom thumbnail upload and the size of the public thumbnail file that a downloader can retrieve from an existing video. They are not the same workflow.
Current custom-thumbnail recommendation
YouTube's current help documentation recommends a 3840 × 2160 image for video thumbnails, with a 16:9 aspect ratio and a minimum width of 640 pixels. For Shorts it recommends 2160 × 3840 with a 9:16 ratio. YouTube also recommends making the custom thumbnail as large as possible because it can be used as the preview image in embedded players.
File-size limits now depend on where you upload. YouTube lists 2 MB for video thumbnails uploaded from mobile and 50 MB for video and Shorts thumbnails uploaded from desktop. That means the old blanket rule that every thumbnail must always stay below 2 MB is no longer accurate.
Why downloaders still show 1280 × 720 MAX RES
A thumbnail downloader is not downloading the original design file that a creator uploaded. It fetches the public thumbnail variants that YouTube exposes for the video. The familiar maxresdefault image is commonly 1280 × 720, followed by SD 640 × 480, HQ 480 × 360, MQ 320 × 180 and Default 120 × 90 when those variants exist.
That is why ThumbPull separates PULL from RESIZE. PULL gives you the public image YouTube serves. RESIZE lets you create a new output canvas such as 1280 × 720, 3840 × 2160 or any custom dimensions you need.
Which size should you actually use?
If you are downloading an existing video's public thumbnail, choose the largest genuine variant that exists and avoid pretending an upscale is a higher-quality source. If you are preparing a new custom thumbnail for upload, work from the highest-quality source you have, keep the composition at 16:9, and use the current high-resolution recommendation when your workflow supports it.
For practical compatibility, 1280 × 720 remains a common editing and publishing canvas across many creator tools. ThumbPull therefore keeps that classic preset while also supporting any larger custom size through the exact-dimensions controls.