Know what a thumbnail has to do
A thumbnail is not a poster. It sits among a dozen others on a phone screen, a few centimeters wide, and a viewer gives it a fraction of a second. It has one job: make the person stop and want to know more. Everything in the prompt should serve that job.
That means one clear subject, high contrast between subject and background, and room for a few words of title. Busy scenes that look rich at full size turn into mush when shrunk. Before you write the prompt, picture the thumbnail at the size of your thumbnail and ask what a viewer would see.
Use the 16:9 frame
YouTube shows thumbnails at 16:9, the same shape as the video. Make the picture wide from the start: open the prompt with "A wide photo of…" or "A 16:9 scene of…" and set 16:9 in the tool. In our gallery, Google Flow returns 16:9 pictures at 1376 × 768 pixels, a little more than the 1280 × 720 that YouTube thumbnails are commonly made at, so no upscaling is needed.
Remember that YouTube puts the video length in the bottom right corner. Keep faces and important objects out of that corner.
Lead with a face or one object
Faces stop the scroll better than anything else, and a clear emotion does it best: surprise, worry, delight, focus. Describe the expression in plain words, such as "wide eyes and an open mouth" or "a confident half smile", and say where the person is looking. A face looking toward your title pulls the eye there.
If the video is about a thing rather than a person, make that thing big. "A giant rusty padlock filling the right half of the frame" reads; "a room full of locks" does not. Close framing is your friend: write "close-up" or "filling the frame".
Leave space for your title
Most creators add the title text themselves in an editor, where they control the font and spelling. Ask the image tool for space, not for words: "subject on the right, plain dark background on the left third, no text". Image tools still misspell longer text, and a wrong letter in a thumbnail looks careless.
If you do want the tool to write a word, keep it to one or two short words in quotation marks, and check every letter before you upload.
Make the colors work hard
Contrast is what makes a thumbnail readable when it is small. A bright subject on a dark background, or a warm subject on a cool background, separates cleanly. Name the colors you want: "a yellow raincoat against a deep blue stormy sky". Avoid asking for a dozen colors; three is plenty.
Rim light, a thin bright edge around the subject, is a classic thumbnail trick because it lifts a person off a dark background. Add "strong rim light" to the light part of the prompt and see the difference.
Example prompts
For a travel vlog: "A wide photo of a young woman on a cliff edge looking out over a turquoise bay, wind in her hair, subject on the right third, empty bright sky on the left, golden hour, no text."
For a tech review: "A wide studio photo of a sleek unbranded smartphone floating at an angle, glowing screen, dark gradient background, strong blue rim light, product on the right, clean space on the left, no logos, no text."
For a history video: "A wide cinematic photo of a lone soldier in an old uniform standing in fog, face lit from one side, dark empty area on the left for a title, no text." Each example names a subject, a side for it, a side for the title and one light.
Keep a consistent look across videos
Viewers who know your channel should recognize your thumbnail before they read the title. Choose a few things that stay the same in every thumbnail prompt: the side the subject sits on, a main color, the type of light and the camera distance. Write those words down and reuse them, changing only the subject for each video.
A consistent look also makes testing fair. When every thumbnail shares the same layout, the difference in clicks between two videos says more about the subject and title than about the design, so you learn which topics your audience wants.
Test it at real size
Before you upload, shrink the picture to about 250 pixels wide and look at it on your phone. Can you tell what it is in one second? Is the face clear? Does the title space still look empty and clean? If not, push the subject closer or simplify the background, and run the prompt again.
PromptRatio's YouTube thumbnail category has tested prompts in this shape, each with the picture it made, so you can start from a layout that already works and swap in your own subject.
Tested prompts on this topic
Every prompt in these categories comes with the picture it made, so you can try the ideas above on a prompt that already works: YouTube Thumbnails, Channel Banners and Reels & Shorts Covers. To trim a finished picture to an exact platform size, use the free crop tool.
