YouTube thumbnail checker

How to check a YouTube thumbnail

1. Drop your image into the box above, or click it to choose a file from your computer or phone.
2. Read the checklist – green means the thumbnail is ready, orange is a warning and red will be rejected or look wrong on YouTube.
3. Look at the previews at the exact sizes YouTube uses on the home feed, in search, on mobile and in the “Up next” list.
4. Fix anything that fails, export again and check the new version.

Already published? Paste the video link instead to check the thumbnail YouTube is showing right now.

YouTube’s thumbnail requirements

For the full list of sizes YouTube creates from your upload, see the YouTube thumbnail size guide.

How to fix the most common problems

• Too large (over 2 MB): export as JPG at 80–90% quality, or run it through the thumbnail resizer, which compresses it under 2 MB automatically.
• Wrong aspect ratio: crop to 16:9 – the resizer can fill or fit the frame for you.
• Low resolution: start from the original design file or a bigger video frame instead of enlarging a small screenshot.
• Low contrast: use a brighter subject, a darker or simpler background, and bold text with an outline or shadow.

Why checking at small sizes matters

Most viewers see your thumbnail at around 320×180 pixels – on a phone often even smaller. Details that look great on your monitor can turn into noise at that size. A good thumbnail still reads clearly in the smallest preview: one subject, three to five words and strong contrast. When you are happy with it, compare it with titles in a realistic feed using the thumbnail preview tool, and read the 10 thumbnail mistakes that cost clicks.

What the contrast check measures

Contrast is the difference between the lightest and darkest parts of your thumbnail. The checker converts the image to brightness values, the same way a black-and-white photo would show it, and looks at how widely they spread. Thumbnails with a bright subject on a dark background, or dark text on a light area, pass easily. Images that are mostly the same tone get a warning, because in a feed full of colourful thumbnails they look dull and are easy to scroll past.

If you get the low-contrast warning:

• Darken or blur the background so the subject pops.
• Add an outline or drop shadow to text.
• Increase saturation slightly – but avoid neon colours on neon backgrounds.
• Check it in greyscale. If the subject vanishes in black and white, it will vanish in the feed too.

A 60-second routine before every upload

1. Run the image through this checker until every row is green.
2. Look at the Up next preview – the smallest size is the hardest test.
3. Write your title in the title counter and make sure title and thumbnail tell one story.
4. Upload in YouTube Studio and open the video on your phone to see the real result.
5. After 48 hours, compare the click-through rate with your recent videos; our guide to YouTube click-through rate explains what is normal.