Short answer: before you upload a thumbnail, check three things: it meets YouTube's technical rules, it still reads at phone size, and it promises the same thing as your title. Most weak thumbnails fail one of these, and you can catch all three in a few minutes with the checklist below.

(Disclosure: this checklist is published by LaunchPad YT, which runs a free feedback forum and a marketplace for expert thumbnail reviews.)

Part 1: The technical basics

These are YouTube's own requirements for custom thumbnails. Check YouTube Help for the current version, as they occasionally change.

1. It's 16:9 and as large as you can make it. YouTube now recommends 3840×2160 for videos, with a minimum width of 640 pixels. (Shorts use 9:16.)

2. The file is JPG or PNG and under the size limit: 2MB if you upload from the mobile app, 50MB from a computer.

3. Your account can use custom thumbnails. You need a verified account, and Community Guidelines strikes can limit uploads.

4. Nothing important sits in the bottom-right corner. YouTube puts the video length there, so text or faces in that corner get covered.

Part 2: Does it read at phone size?

Most viewers first see your thumbnail as a small rectangle in a feed or a sidebar.

5. Shrink it and look again. View it at roughly the size it appears on a phone home feed. If you can't tell what it shows within a second, simplify it.

6. There is one clear focal point. One face, one object or one idea. Three competing elements usually become noise at small sizes.

7. Text is short or absent. If you use text, a few large words are easier to read than a sentence, and they shouldn't repeat the title word for word.

8. It stands out against YouTube's interface. Check it on both light and dark mode. Thumbnails that are mostly white or mostly black can blend into the page.

Part 3: Does it match the video?

A thumbnail that gets the click but doesn't match the video leads to viewers leaving early, which hurts the video more than a lower click-through rate.

9. Title and thumbnail work together. The thumbnail shows the situation; the title adds what the image can't. Read them side by side as one promise.

10. The video delivers the promise in the first 30 seconds. If the thumbnail shows a result, a reaction or a scene, viewers should see it, or a clear path to it, early on.

11. It fits your channel. A returning viewer should recognise it as yours, through a consistent colour, layout or style, without every thumbnail looking identical.

Part 4: Get a second opinion

12. Someone else has seen it at small size. You already know what the video is about, so you can't judge whether a stranger understands the thumbnail at a glance. A quick second opinion catches what you can't see.

Options for that second opinion:

  1. Friends who watch your genre. Free and fast, but often too polite.
  2. Creator communities, such as r/NewTubers or the LaunchPad YT forum, where you can post a thumbnail and get comments from other creators for free.
  3. An experienced YouTuber in your niche. On LaunchPad YT, you can book an expert review with thumbnail feedback as an add-on (for example, up to 3 thumbnails for 50 credits; 100 credits cost $19.99), or order a custom thumbnail made by an expert, with credits held until you accept it.
  4. YouTube's Test & Compare, after publishing. If it's available on your channel, you can upload up to three thumbnails and let YouTube test them on real viewers. It answers "which one?", but only once the video is live.

For a deeper guide to the options, see where to get honest YouTube thumbnail feedback, and if you'd rather have someone make it, how to hire someone to make your YouTube thumbnail.

The checklist, copy-paste version

  1. 16:9, at least 640px wide (3840×2160 recommended)
  2. JPG or PNG, under 2MB (mobile) or 50MB (desktop)
  3. Account verified for custom thumbnails
  4. Bottom-right corner clear of key details
  5. Readable at phone size
  6. One focal point
  7. Few or no words, not repeating the title
  8. Stands out in light and dark mode
  9. Title and thumbnail make one promise
  10. Video delivers it early
  11. Recognisably your channel
  12. Someone else has checked it

Get feedback on your thumbnail

Not sure your thumbnail works? Post it on the LaunchPad YT forum for free feedback from other creators, or book an experienced YouTuber to review it before you upload.