YouTube thumbnails: 16:9, JPG/PNG/WebP, under 2MB. Baseline 1280×720; upload 3840×2160 (4K) for the sharpest result: the higher resolution matters most on TV apps, where thumbnails render large and 720p softens. This tool outputs the 4K spec, auto-fitted under the 2MB cap, with the finished size shown per file.
Rules that matter more than the spec:
- Design for 200 pixels wide: that's how most viewers meet a thumbnail (search results, sidebars, phone feeds). Faces, bold shapes, three words or fewer survive the shrink; sentences and screenshots don't.
- Leave the bottom right corner clear: the duration stamp is drawn over it, and anything you need read belongs nearer the centre.
- Sources that aren't 16:9 get cropped to cover, never stretched. The crop position slider chooses which region survives.
About the 2MB limit: it applies to custom thumbnails in YouTube Studio, and a high-quality 4K JPG can exceed it. Quality here is lowered only as far as the cap requires.
The duration badge sits over the bottom right corner of every thumbnail. Keep faces and words out of that square.
Drop several candidates, download, and judge them at small size before choosing.