What are YouTube's current custom thumbnail specs for videos, Shorts and podcasts (sizes, ratios, desktop vs mobile limits, the 4:5 crop)?

Problem: preparing thumbnail files. Source: YouTube Help 'Add custom thumbnails on YouTube', read 2026-10-23. Source statements: recommended resolution 3840x2160 for videos and 2160x3840 for Shorts (minimum width 640 px for videos, minimum height 640 px for Shorts); JPG or PNG; file limits depend on device: mobile 2 MB for video thumbnails (10 MB for podcasts), desktop 50 MB for video, Shorts and podcast thumbnails; aim for 16:9 for videos, 9:16 for Shorts and 1:1 for podcast playlists. A vertical video with a 16:9 custom thumbnail is replaced by an auto-generated 4:5 thumbnail on the home, explore and subscription pages; the custom one still appears on watch feed, history and non-mobile platforms. Custom Short thumbnails can currently be added only in Studio on a computer and need a verified account; changes may take time to show. This matches the 50 MB desktop limit that the Oct 2025 TV blog said was coming (see P-L4-6-12). Method (inference): design a Short thumbnail at 9:16, check how a 4:5 crop treats text near the edges, and keep key content centred. Limitations: no data on whether a custom thumbnail changes performance (see C3-B573-04 and P-L4-5-15). Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Undated help page; limits may change. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://support.google.com/youtube/answer/72431?hl=en",
      "note": "Image size & resolution; Image size & resolution; Image size & resolution; Note"
    }
  ]
}