Free YouTube tool
YouTube Thumbnail Size Checker
YouTube recommends 3840 x 2160 at 16:9 for a thumbnail, at least 640 pixels wide. Set it from a computer and the cap is 50 MB; set it from the mobile app and it is 2 MB.
Last updated: 2026-10-25
A YouTube thumbnail has to be 16:9, at least 640 pixels wide, and a JPG or PNG. YouTube recommends 3840 x 2160, and the file can be up to 50 MB when you set it from a computer.
The mobile app is stricter. Setting a video thumbnail from the YouTube app caps the file at 2 MB, so a large PNG that goes through from a laptop can be refused on a phone. The checker flags anything over 2 MB as a warning for that reason, not as a rejection.
Custom thumbnails need a verified YouTube account. When Postify publishes a video it sets your cover image as the thumbnail, fitted to 1280 pixels on the long edge and under 2 MB. Drop an image in below and it is measured in your browser, without uploading anything.
Your file never leaves your browser. The dimensions are read on your device and nothing is uploaded to us.
Pick a file and every YouTube format is checked against it at once.
The full spec sheet is below, so you can read the numbers without uploading anything.
YouTube video and image specs
Every YouTube surface with its own limits, in one place. These are the platform ceilings, so an upload that clears them still has to clear whatever your publishing tool allows.
YouTube Short
| Max file size | 256 GB |
|---|---|
| Duration | 1 second to 3 minutes |
| Recommended size | 1080 x 1920 |
| Aspect ratio | 9:16 recommended, 1:2 to 1:1 accepted |
| File types | MP4, MOV, WEBM |
- There is no separate Short upload: a video becomes one automatically when it runs 3 minutes or less and is square or taller.
- The same 256 GB upload ceiling applies, so file size is never what stops a Short.
YouTube Standard video
| Max file size | 256 GB |
|---|---|
| Duration | 1 second to 12 hours |
| Recommended size | 1920 x 1080 |
| Minimum size | 426 x 240 |
| Aspect ratio | 16:9 recommended, 1:2 to 1.78:1 accepted |
| File types | MP4, MOV, AVI, WMV, WEBM |
- 256 GB or 12 hours, whichever you reach first. Uploads longer than 15 minutes require a verified account.
- YouTube recommends roughly 8 Mbps for 1080p and 12 Mbps at 60 fps, and re-encodes everything on the way in.
YouTube Thumbnail
| Max file size | 50 MB |
|---|---|
| Recommended size | 3840 x 2160 |
| Minimum size | 640 pixels wide |
| Aspect ratio | 16:9 only |
| File types | JPG, PNG |
- Setting the thumbnail from the YouTube mobile app caps it at 2 MB, against 50 MB from a computer, so export JPG if you plan to set it from your phone.
- Custom thumbnails need a verified YouTube account. When Postify publishes a video it sets your cover image as the thumbnail, fitted to 1280 pixels on the long edge and under 2 MB.
Specs verified 2026-07-31. Networks adjust these without announcing them, so re-check anything you are about to build a whole shoot around.
YouTube export tips
- Export JPG if you plan to set the thumbnail from your phone. A detailed PNG passes the 2 MB mobile cap easily, and a JPG of the same image usually does not.
- Crop to exactly 16:9 before you upload. That is the shape YouTube asks for, and the checker treats anything else as a mismatch.
- Shorts use a different shape. A Shorts thumbnail is 2160 x 3840 at 9:16, so a 16:9 video thumbnail is not the file to reuse there.
Frequently asked questions
What size should a YouTube thumbnail be?
YouTube recommends 3840 x 2160 at 16:9, with a minimum width of 640 pixels, saved as a JPG or PNG.
What is the YouTube thumbnail file size limit?
50 MB when you set the thumbnail from a computer, and 2 MB when you set it from the YouTube mobile app. Export JPG if your file is close to the mobile cap.
Why can I not add a custom thumbnail?
Custom thumbnails need a verified YouTube account. Once the account is verified, the size rules above apply.
Does this tool upload my image?
No. The image is read in your browser through a temporary link and measured there. Nothing reaches Postify or YouTube.
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