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 real final 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.
- Surrender the bottom-right corner — the video duration stamp overlays it on every listing. Keep all essentials inside the centre region.
- 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.
Drop several candidates, download, and judge them at small size before choosing. Everything runs in this page on your device — the file goes from here straight to YouTube Studio, no server in between.