What is a thumbnail?

Also called video thumbnail, cover image, reel cover.

A thumbnail is the small preview image that represents a video or link before someone opens it, such as a YouTube video's image in search results or a reel's cover on your profile grid.

Why it matters

On YouTube especially, the thumbnail and title are most of what people judge before deciding to click. On Instagram and TikTok, covers shape how your profile grid looks to a new visitor. A clear, honest thumbnail gets more of the right people to watch; a blurry auto-picked frame or a misleading one does the opposite.

Example

A cooking channel's thumbnail shows the finished biryani in close-up, filling most of the frame, with three large words, "30-minute biryani", and the cook's face to one side.

YouTube thumbnail requirements

YouTube's help centre gives these guidelines for custom thumbnails. You can only upload your own thumbnail once your account is verified; otherwise you choose from the frames YouTube picks.

  • Recommended resolution: 3840 x 2160 pixels for videos and 2160 x 3840 for Shorts.
  • Minimum: 640 pixels wide for videos, 640 pixels tall for Shorts.
  • Aspect ratio: 16:9 for videos, 9:16 for Shorts.
  • Formats such as JPG or PNG.
  • File size: up to 2 MB when uploading from a phone, and up to 50 MB from a computer.
  • Shorts thumbnails can only be added in YouTube Studio on a computer.
  • Thumbnails must follow YouTube's Community Guidelines.

Reel and TikTok covers

On Instagram, you can pick a cover for a reel from a frame of the clip or upload a separate image from your device. TikTok also lets you choose a cover before posting. Because the profile grid shows a cropped preview, keep the main subject and any words in the centre of the cover.

How to design a thumbnail people click

A thumbnail is seen small, often at the size of a fingertip, next to other options.

  1. Show the result or the most interesting moment, not the opening frame.
  2. Use one clear subject: a face, a product or a finished dish.
  3. Add no more than a few large words, if any, and make sure they don't just repeat the title.
  4. Use strong contrast so it stands out against a white or dark background.
  5. Check it at phone size before publishing.
  6. Make sure the video delivers what the thumbnail promises.

Thumbnails beyond video

Link previews are thumbnails too. When you share a link to your website on Facebook, LinkedIn or X, the platform shows an image taken from the page, usually the one your website marks for sharing. If the preview shows the wrong image or none at all, ask whoever manages your website to set a share image for that page. On Pinterest, the Pin image itself does the job of a thumbnail, so a clear, upright image with the main subject easy to see matters just as much as on YouTube.

Common questions

Why can't I upload a custom thumbnail on YouTube?

Your account needs to be verified. Until then, YouTube only lets you choose from the thumbnails it generates automatically from the video.

What size should a YouTube thumbnail be?

YouTube recommends 3840 x 2160 pixels at 16:9 for videos, with a minimum width of 640 pixels, in a format such as JPG or PNG. Files can be up to 2 MB from a phone or 50 MB from a computer.

Is it OK to use a dramatic thumbnail?

Bold is fine; misleading isn't. If the video doesn't deliver what the thumbnail suggests, viewers leave quickly, and YouTube can remove thumbnails that break its Community Guidelines.

Source: YouTube Help: Add video thumbnails, checked 14 October 2026

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