Keep the 16:9 canvas
YouTube's help page recommends 16:9 for videos. It does not give a fixed numeric phone-or-TV crop map for standard video thumbnails.
YOUTUBE CREATOR GUIDE 01
YouTube thumbnail size
For a video thumbnail, YouTube currently recommends 3840 × 2160 pixels, a 16:9 aspect ratio, and a minimum width of 640 pixels. YouTube lists JPG and PNG among the supported image formats.
Source: YouTube Studio Help — Add custom thumbnails
Recommended resolution3840 × 2160Video thumbnail
Aspect ratio16:9For videos
Minimum width640 pxYouTube Help wording
Upload limit2 MB / 50 MBMobile / desktop video upload
VIDEO THUMBNAIL
The numbers to check before upload
01
Canvas: 3840 × 2160 pixels is YouTube's current recommendation for video thumbnails.
02
Shape: Use 16:9 for a standard video thumbnail. The official page says to try this aspect ratio for videos.
03
Format: JPG or PNG are listed by YouTube. The official page says “such as,” so this page does not claim that the list is exhaustive.
04
File size: The current page states 2 MB for mobile video thumbnails and 50 MB for desktop video, Shorts, and podcast thumbnails.
SURFACE CHECK
What changes on mobile and Shorts?
Home, Explore, and subscriptions can use 4:5
For vertical videos with a 16:9 custom thumbnail, YouTube says an auto-generated 4:5 thumbnail replaces it on those surfaces. The custom thumbnail still appears on the watch feed, watch history, and non-mobile platforms.
Use a vertical 9:16 brief
YouTube recommends 2160 × 3840 pixels for Shorts, with a minimum height of 640 pixels. Custom Shorts thumbnails are currently added in YouTube Studio on a computer.
SOURCE NOTES
What YouTube Help does and does not specify
FOUND Video recommendation, minimum width, ratios, listed formats, upload limits, Shorts resolution, and the 4:5 vertical-video surface rule are stated on the official thumbnail help page.
NOT FOUND A fixed pixel crop boundary for a standard thumbnail on TV or phone surfaces is not stated on that page, so this guide does not invent one.