What the YouTube thumbnail checker looks at
The checker reads the file you add and compares it with the published requirements for custom thumbnails. It reports five things: resolution, aspect ratio, file size, format and the bottom-right corner. Each one gets a label and one sentence about what to do next.
- Pass. The file meets the requirement. You don't need to do anything.
- Check. The file is allowed, but something is worth a second look, such as a size smaller than the recommended one.
- Fix. The file is outside the limit. Change it before you upload.
Open the panel at the top of the tool, add a thumbnail and the rows fill in at once. If you add more than one version, click a version in the preview to choose which one is checked.
YouTube thumbnail size and other requirements
These are the values the checker uses, taken from the YouTube Help page and listed with what the checker does for each.
| Setting | Official value | What the checker does |
|---|---|---|
| Resolution | 3840 × 2160 recommended; minimum width 640 px | Pass at 3840 × 2160 or larger, Check between that and 640 px wide, Fix under 640 px |
| Aspect ratio | 16:9 | Pass when width divided by height is 1.778, give or take half a percent; Fix otherwise |
| File size | 2 MB or less from a phone; 50 MB or less from a desktop | Pass at 2 MB or less, Check up to 50 MB, Fix above 50 MB |
| Format | JPG or PNG | Pass for JPG and PNG; Fix for anything else, including WebP |
| Bottom-right corner | Not a rule; the length badge sits here | Always Check, as a reminder to keep key content out of the corner |
Source: YouTube Help, support.google.com/youtube/answer/72431. Checked on 2026-10-25. YouTube can change these limits, so confirm them on the official page before a big upload.
How to fix what the checker flags
The aspect ratio is not 16:9
Open the image in your editor and set the canvas to 16:9, for example 1920 × 1080 or 3840 × 2160. Rebuild the layout on the new canvas instead of stretching the old one, because stretched faces and text are easy to spot.
The file is too large
Export as JPG at a slightly lower quality. Photos compress well as JPG. Flat graphics with sharp text can look cleaner as PNG but are often larger. Aim for 2 MB or less if you plan to upload from the phone app.
The format is not JPG or PNG
Export or convert the image to JPG or PNG. WebP files open in this checker so you can preview them, but they are not on the official list.
The resolution is smaller than recommended
A Check on resolution means the image clears the 640 pixel minimum but not the recommended 3840 × 2160. If your source file is larger, export it at full size. If it is not, upload what you have rather than stretching it, since enlarging a small image only makes it soft.
How to use the checker
- Add the file. Choose it, drop it on the page or paste it from the clipboard.
- Read the five rows. Fix anything marked Fix, and decide whether the Check items matter for your video.
- Look at the preview. A file can pass every line and still look weak in the feed, so switch through the views under the checker.
- Export again and re-check. Add the new file and confirm every row before you upload to YouTube.
The bottom-right corner
This is the one row that is never a Pass, because it is not a rule at all. Most videos show their length in a small dark badge at the bottom right of the image. Turn on Show badge area in the tool to draw a translucent box over that spot. If a face, a word or a logo sits under the box, move it. The box is a guide, so leave a little extra room.
What the checker cannot tell you
It checks the file, not the idea. It cannot say whether the image will earn clicks, and it does not review the image against YouTube's content policies, which you can read on the official site. It also cannot see how your channel's audience will react. For that, put the image in context with the home view and the small view, and compare versions on the tester page.
YouTube thumbnail checker FAQ
Why does my image show Check for resolution?
Check means the image is at least 640 pixels wide, which is the minimum, but smaller than the recommended 3840 × 2160. It is allowed. The label only points out the gap so you can export a larger file if your source allows it.
Does the checker upload my file?
No. The file is read inside your browser, and the width, height, size and type are worked out on your device. Nothing is sent to a server and nothing is saved.
Why is 2 MB the line for file size?
YouTube's help page lists 2 MB as the limit for uploads from a phone and 50 MB from a desktop. The checker marks anything over 2 MB as Check so you notice before you upload from a phone, and anything over 50 MB as Fix.
Is the badge overlay exact?
No. It is a guide that shows roughly where the length badge sits. The real badge changes size with the device and the text inside it, so leave extra space around anything important.
Limits of this checker
- It follows the YouTube Help page as it read on 2026-10-25. Requirements can change.
- The previews are illustrations, not exact copies of YouTube's pages. Real layouts change by device, app version and over time.
- It reads file properties your browser reports. A file with a wrong extension is judged by its real type.