The short answer
1280 by 720 pixels, 16:9, under 2MB, saved as JPG or PNG. That is the whole specification. Everything below is about why each number is there and what goes wrong when you ignore it.
Why 1280x720 and not something larger
YouTube stores one high-resolution thumbnail per video, called maxresdefault, and it tops out at 1280x720. Upload a 4K image and YouTube accepts it, then scales it down to 1280x720 for storage. There is no 1080p or 4K thumbnail to retrieve later, which surprises people who go looking for one. If you want to see what YouTube actually kept, pull it with our YouTube thumbnail downloader and compare it to your source file.
Uploading larger than 1280x720 is still worth doing when your source is a photograph, because downscaling sharpens detail. Uploading smaller is not: YouTube will not upscale, and a 640x360 thumbnail looks soft on a desktop home feed.
The 2MB limit is the one that actually blocks uploads
YouTube rejects thumbnails over 2MB outright. This bites hardest on PNG exports, because PNG is lossless and a busy thumbnail with a photographic background can easily land at 3 to 5MB at 1280x720. Two fixes, in order of preference:
- Export as JPG at quality 85 or so. At thumbnail sizes the difference is invisible and the file drops to a few hundred KB.
- Compress the PNG if you need the transparency or the crisp text edges. Our image compressor will take a 4MB PNG under the limit without touching the dimensions.
Where the 16:9 frame actually gets cropped
Your full 16:9 image is shown in the home feed and in search results. It is not shown intact everywhere. Two places to watch:
- Shorts are a 9:16 vertical format, so a 16:9 thumbnail gets centre-cropped hard. If you publish Shorts, design a separate vertical image rather than reusing the horizontal one.
- The watch-page sidebar renders around 168 pixels wide. Anything you put in the outer fifth of the frame is competing with the title text next to it for attention.
The practical rule is to keep faces and text inside the middle 80% of the frame, and treat the edges as decoration you can afford to lose.
Text size: design for the smallest render, not the largest
A thumbnail that is legible on your monitor at full size can be unreadable in the mobile feed, where it renders at roughly 160x90. That is an eighth of the linear size you designed at. As a working threshold, text below about 80pt at 1280x720 stops being readable on a phone.
Most mobile viewers also run dark mode, so a thumbnail with a white background sits in a bright rectangle against a near-black page. That can work as a deliberate contrast play, and it can also look like a rendering error. Check it before publishing rather than after.
File format, briefly
YouTube accepts JPG, PNG, GIF and BMP. In practice use JPG unless you have a reason not to. PNG is worth it for flat-colour designs with hard-edged text, where JPG compression puts visible artefacts around the letters. GIF and BMP have no advantage here.
A checklist before you hit upload
- 1280x720, or a larger 16:9 image you are happy to have downscaled
- Under 2MB, which usually means JPG
- Key elements inside the middle 80%
- Text large enough to read at 160x90
- Checked against a dark background if your design is light
If you want to see a design in the contexts YouTube actually renders it, our thumbnail previewer shows the feed, search, sidebar and mobile sizes side by side.