YouTube tools
Thumbnail Size Checker
Check thumbnail dimensions, aspect ratio, and file details in your browser.
- Free
- No upload
- Runs in your browser
Check your thumbnail
Select an image to see its dimensions, aspect ratio, file size, and current YouTube thumbnail compatibility.
How to use
- Select or drag a JPG or PNG image into the drop zone above.
- Review the width, height, aspect ratio, and file size YouTube will see.
- Check each pass/warning/fail result and fix anything flagged before uploading.
YouTube thumbnail guidelines
This checker verifies your image against YouTube's current published requirements for standard custom thumbnails:
- Format: JPEG or PNG
- Width: 640px minimum, 3840px recommended
- Aspect ratio: 16:9 for standard videos
- File size: up to 2.00 MB from the mobile app, up to 50.00 MB from the web
What the results mean
- Pass— meets YouTube's current guidance; no action needed.
- Warning — usable, but not ideal. Review it before you upload.
- Fail — likely to cause a problem on upload or display. Fix it first.
Methodology and limitations
This tool checks your image against YouTube's current published custom-thumbnail guidance for standard videos: file format, minimum/recommended width, recommended 16:9 aspect ratio, and mobile vs. web upload file-size limits. Dimensions and format come from what your browser reports for the file you selected. YouTube can change these requirements at any time, and YouTube may apply additional checks at upload time that this tool cannot see.
FAQ
Does this tool upload my image anywhere?
No. Your image is analyzed entirely in your browser and is never sent to a server.
Why did a correctly sized image still get a warning?
A warning means the file is usable but not optimal — for example, a width below YouTube's recommended (but above the minimum) resolution, or an aspect ratio other than 16:9.
Can this guarantee YouTube will accept my thumbnail?
No. YouTube applies its own checks at upload time, and requirements can change. Use this tool as a pre-upload sanity check, not a final guarantee.
Source
Rules on this page are checked against YouTube's own custom-thumbnail documentation, not third-party advice.
support.google.com — Add a custom video thumbnailVerified 2026-08-20. YouTube can change these requirements at any time.