What to check in the preview
The smallest size. In the sidebar and on many phones, a thumbnail is shown about 168 px wide, under a seventh of its real width. If you can't read the text or tell what's happening there, the thumbnail is too busy. Three or four words in big, heavy letters is the usual ceiling.
The timestamp corner. YouTube puts the video length over the bottom-right corner, so keep faces and text out of it. Both themes. Most viewers use dark mode, where dark-edged thumbnails can melt into the page; a light border or a bright subject helps. Title and thumbnail together. They should add to each other, not repeat the same words.
YouTube thumbnail requirements (2026)
| Spec | Requirement |
|---|---|
| Aspect ratio | 16:9 |
| Size | 1280 × 720 is the long-standing standard; YouTube now recommends up to 3840 × 2160. Minimum width 640 px. |
| File size | 2 MB when uploaded from a phone, 50 MB from a computer |
| Formats | JPG, PNG, GIF (first frame) or BMP |
Custom thumbnails need a verified channel, and there's a daily limit on how many you can upload. Use the social media image resizer to export at exactly 1280 × 720 under 2 MB, and YouTube's built-in Test & Compare to A/B test the versions you like here.
Frequently asked questions
What size is a YouTube thumbnail?
1280 × 720 pixels (16:9) is the standard, at least 640 px wide. YouTube now recommends up to 3840 × 2160. The file must be under 2 MB from a phone or 50 MB from a computer.
How can I test my thumbnail before uploading?
Drop it here to see it in the home feed, on a phone and at sidebar size in both themes, next to up to two other versions. Then use YouTube's Test & Compare to run a real A/B test.
Is my thumbnail uploaded?
No. The preview is built in your browser, and the image never leaves your device.
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