YouTube thumbnail tester: preview, check and resize
Preview a thumbnail in YouTube’s feed, search and Up next, light or dark, check it against YouTube’s rules and export a ready copy. Free; nothing is uploaded.
By Mellow · UpdatedTest your thumbnail
What size is a YouTube thumbnail in 2026?
YouTube’s help asks for 3840 × 2160 pixels at 16:9, at least 640 pixels wide, as a JPG or PNG. The file can be up to 2 MB from a phone and 50 MB from a computer. A Shorts thumbnail is 2160 × 3840 at 9:16, at least 640 pixels tall, and can be added only in YouTube Studio on a computer. Custom thumbnails need a verified account. We read these on October 1, 2026 on YouTube’s own page; many guides still quote the older 1280 × 720 and 2 MB.
YouTube’s requirements at a glance
| Video | Short | |
|---|---|---|
| Recommended size | 3840 × 2160 | 2160 × 3840 |
| Shape | 16:9 | 9:16 |
| Minimum | 640 pixels wide | 640 pixels tall |
| Formats | JPG or PNG | |
| File size | Up to 2 MB from a phone, 50 MB from a computer | |
| Where to add it | YouTube Studio or the YouTube app | YouTube Studio on a computer |
| Who can | Verified accounts | |
Podcast playlists take a square, 1:1 thumbnail instead. Source: YouTube Help: Add custom thumbnails on YouTube, read on October 1, 2026.
Why test at the smallest size first
The same thumbnail is shown large on the home feed and on a TV, and small beside a playing video, where the Up next list draws it about 168 pixels wide on a computer. What survives there is what gets noticed: one subject, a face or an object, and three or four words at most. Fine print and small logos disappear first. The tester draws every surface side by side so you can see that before you upload.
- Leave the bottom-right corner clear. The video’s length covers it on every surface.
- Check dark mode. A thumbnail with a black or white edge melts into one of YouTube’s two backgrounds.
- Compare against real neighbours. Paste links of videos you compete with: a thumbnail that looks bold alone can look like all the others in a row.
- Keep the promise. YouTube’s own thumbnail and title tips ask for thumbnails and titles that match the video, so viewers don’t leave early.
Then let YouTube pick the winner
A preview cannot tell you which thumbnail people click. YouTube Studio can: its A/B test shows up to three titles and thumbnails to viewers, compares their share of watch time and shows the winner to everyone, usually within two weeks. It runs on a computer, for channels with advanced features, and not for Shorts. Use this tester to decide which three versions deserve the test.
Questions
What size should a YouTube thumbnail be?
YouTube’s help asks for 3840 × 2160 pixels at 16:9, at least 640 pixels wide, as a JPG or PNG. We read that on October 1, 2026. A Shorts thumbnail is 2160 × 3840 at 9:16, at least 640 pixels tall.
Is 1280 × 720 still fine for a YouTube thumbnail?
Yes. It is well above YouTube’s 640-pixel minimum and looks sharp on phones and computers, and it stays under the 2 MB limit for uploading from a phone. YouTube’s help now recommends 3840 × 2160, which shows on large screens and TVs.
What is the maximum file size for a YouTube thumbnail?
2 MB when you upload from a phone and 50 MB from a computer, according to YouTube’s help. Many guides still quote 2 MB for every upload, which was YouTube’s older limit.
Why can’t I add a custom thumbnail?
YouTube lets only verified accounts add custom thumbnails. Shorts thumbnails can be added only in YouTube Studio on a computer. If the option is missing, verify the account in YouTube’s settings and try again from a computer.
How do I know which thumbnail works better?
Run YouTube Studio’s own A/B test: it shows up to three titles and thumbnails to viewers and keeps the one with the highest share of watch time, usually within two weeks. It works on a computer, and not for Shorts. This tester helps you choose what goes into that test; it cannot measure clicks.
Is my thumbnail uploaded anywhere?
No. The image stays in this page and the download is made in your browser. Only the videos you add for comparison load from YouTube’s image server.
Make the thumbnail and upload the video with Mellow Hub
Hub’s Creative Studio makes a 16:9 cover at 1280 × 720 from a short brief, and Hub uploads the video to YouTube with that cover, on its own or together with Shorts, Reels and TikTok. It checks YouTube’s 100-character title limit before anything is sent. See YouTube videos and thumbnails for the steps.
See the Creative StudioThis tool is free and needs no account. Mellow Hub is paid, after a 7-day free trial, and publishes only what you, or an assistant you have authorised, send or schedule.
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