See your thumbnail the way viewers will: tiny, surrounded by other videos, and often in dark mode. Drop in up to three candidates, add the title, and compare them across YouTube's real surfaces before you upload anything.
Tiles are drawn at the sizes YouTube renders on a desktop viewport; gray tiles are neutral placeholders standing in for other videos. Scroll sideways on a small screen.
How it works
Drop in one to three thumbnail images and the page renders each one, labelled A, B, and C, inside mock YouTube layouts built to the platform's real rendered sizes. That is roughly 360 x 202 in the desktop home grid and search results, and 168 x 94 in the watch-page sidebar. In the mobile feed it fills the phone's width. In the Shorts shelf it becomes a 9:16 crop. Neutral gray placeholder tiles stand in for the videos around it, so you judge the thumbnail in context. The dark-mode toggle shows both themes. The title, channel name, and duration badge you type appear on every tile.
Each upload card runs the checks that need no judgement. Is the aspect ratio 16:9? Is the width at least 640 pixels? And does the file size fit the 2 MB mobile and 50 MB desktop upload limits? The Measure text button opens the image large. Drag a box over your biggest text and the tool converts its height to the 720-pixel-frame equivalent. It warns below 24 pixels and shows how tall that text ends up in the home grid and the sidebar.
Download comparison sheet saves a single PNG with every candidate at three rendered sizes, handy for sharing with an editor or client. Everything runs in your browser, and the images never leave it. When a candidate fails the size checks, the YouTube Image Resizer fixes it. The YouTube Thumbnail Downloader pulls a published video's current thumbnail in for comparison.
What you will see
- A / B / C chips
- Which uploaded candidate a tile shows. The same letters label the upload cards and the comparison sheet.
- Surface pills
- The five mock layouts: desktop home grid, search results, watch-page sidebar, mobile home feed, and the Shorts shelf.
- Ratio / width / size chips
- Pass or warning against the 16:9 ratio, the 640-pixel minimum width, and the 2 MB mobile and 50 MB desktop upload limits.
- Measure text
- Drag a box over the biggest text in the image. The tool reports its height scaled to a 720-pixel frame, where 24 px is the readability floor, and its rendered height in the home grid and sidebar.
- Dark mode
- The same surfaces on YouTube's dark palette, which a large share of viewers use.
- Comparison sheet
- A downloadable PNG with each candidate at 480, 240, and 120 pixels wide.
Frequently asked questions
How do I test a YouTube thumbnail before uploading it?
Drop the image, or up to three candidates, into this page. Type the video title and your channel name. The tester draws each one into mock YouTube layouts at the sizes YouTube really renders: the desktop home grid, search results, the watch-page sidebar, the mobile feed, and the Shorts shelf. Neutral gray placeholder tiles stand in for the videos around it. Flip between light and dark mode, because half your audience sees the dark one. Nothing is uploaded and no account is needed.
What sizes does YouTube actually show thumbnails at?
Far smaller than the file you upload. A 1280 x 720 thumbnail is usually rendered around 360 x 202 in the desktop home grid and search results, and around 168 x 94 in the watch-page sidebar. In the mobile feed it fills the phone's width, roughly 360 to 400 CSS pixels. That is why this page judges your image at those sizes instead of full screen. A design that only works large fails where most impressions happen.
How is this different from YouTube Studio's "Test & compare"?
Studio's built-in A/B test is the gold standard for measuring real click-through rate. But it needs the video to be published and takes days to reach a result. This tester works before upload. You see the candidates side by side in realistic surroundings and rule out the ones that fail at small sizes. Then let Studio's experiment pick between the finalists that survive.
What makes a thumbnail readable at small sizes?
Three things carry most of it. Text height: a good rule is that any text should be at least 24 pixels tall in the 720-pixel-high frame, which is what the Measure text check verifies. Strong contrast between subject and background. And restraint: three to four words at most, with one clear focal point. A face with visible emotion and a single bright accent colour survive shrinking better than a busy scene.
What are the thumbnail requirements?
A 16:9 aspect ratio with a minimum width of 640 pixels. YouTube's help page recommends up to 3840 x 2160, and 1280 x 720 remains the standard size most creators upload. Formats are JPG or PNG, with an upload limit of 2 MB on mobile and 50 MB on desktop. The checks on each upload card verify the ratio, the minimum width, and which file-size limit you fit under. The YouTube Image Resizer fixes a file that fails them.
Can I A/B test thumbnails on this page?
You can compare up to three candidates side by side in every surface. That is an eyeball A/B test. It reliably catches the version whose text vanishes or whose subject gets lost at 168 pixels wide. It does not measure clicks. For a statistical winner, upload your best two or three and run YouTube Studio's "Test & compare" on the published video.
Are my images uploaded anywhere?
No. The previews, the checks, and the comparison sheet are all built in your browser. The images never leave your device, and there is no signup and no watermark. Reload the page and they are gone.
Why does my thumbnail look cropped in the Shorts shelf?
Because the Shorts shelf uses vertical 9:16 tiles. A 16:9 thumbnail shown there is cropped to a narrow slice around the centre. If the video is a Short, make a dedicated vertical image instead of reusing the widescreen one. The recommended size is 2160 x 3840, with a minimum height of 640. The YouTube Image Resizer has a Shorts preset. The shelf preview exists to show you this crop before it surprises you.