The thumbnail test
Here is the uncomfortable arithmetic. Your cover is 1,900 pixels wide when you design it. On a phone, in a list of search results, it is displayed at about 100 to 160 pixels tall — roughly the size of a postage stamp, and about one-twelfth of the size you've been staring at.
Almost every purchasing decision starts there. The full-size cover is something a reader sees after they've already decided to look closer.
So the thumbnail isn't a compromised version of your cover. It is your cover. The big one is a bonus.
In the Cover Maker — you don't have to fake this. Press Cover check… in the Cover Maker. It renders your finished front cover at the two sizes stores actually display — about 160 px for a search result and 100 px for a recommendation strip — plus a grayscale panel that exposes the value-contrast problem below. It uses the real cover, title and all, not the raw artwork. Start a book → · about the Cover Maker
Running the test
You don't need a tool. You need thirty seconds.
- Export or screenshot your front cover.
- Scale it down until it's about 1.5 cm / half an inch tall on your screen. On a laptop that's roughly 160 pixels.
- Look at it from normal reading distance — don't lean in.
- Now answer three questions honestly.
Can you read the title? Not "can you make it out because you already know what it says" — genuinely read it, as a stranger would.
Can you tell the genre? Squint until the detail disappears. Is this obviously a thriller, a romance, a memoir? If it could be four things, it's none of them.
Does one thing dominate? Or does it dissolve into visual soup?
Anything you have to lean in for is a fail. Readers do not lean in. They scroll.
Two harder versions of the same test
The grid test. Put your thumbnail next to nine real covers from your category and look at all ten together. This is closer to how readers actually encounter your book — never alone, always in competition. Covers that look fine in isolation often disappear completely in a grid, and you'll see instantly which of the ten your eye goes to.
The grayscale test. Desaturate the thumbnail. If your title vanished when the color left, you were relying on hue contrast rather than value contrast — a common and expensive mistake, and one that also matters for print. See Color and contrast.
What usually fails
The title is too small. By far the most common. At full size a modest title looks elegant and restrained. At thumbnail it's gone. Professional covers routinely run type far bigger than feels comfortable when you're zoomed in — often 70–80% of the cover's visual weight.
The title sits on busy artwork. Type needs a calm area to live in, and detailed illustration underneath destroys legibility at small sizes even when it looks fine large. Fix it by designing space for the title from the start rather than hunting for a gap afterwards — Composition and negative space.
Thin or decorative lettering. Hairline serifs, script faces and heavily ornamented display type lose their strokes entirely when shrunk. Save decorative faces for a short title, or use them for the series line and set the title in something sturdier.
Too many elements. Four things at full size is cluttered. Four things at thumbnail is a gray smudge.
Low contrast. Pale type on a pale sky. Dark type on a dark forest. It reads at 1,900 pixels and disappears at 160.
The fix is usually one of three things
In order of how often they work:
- Make the title bigger. Much bigger than feels right. Then bigger again.
- Give it somewhere to sit — a darker area of sky, a flat band of color, a simplified region of the art.
- Cut something. Almost every failing cover has one element too many. Removing it is free and usually fixes the whole thing.
Do this before you finish, not after
The thumbnail test is worth running at the sketch stage, when changing the composition costs nothing. Most authors run it at the end, discover the problem, and then try to rescue a finished image by nudging the title around — which rarely works, because the problem is the composition, not the placement.
If you're generating your artwork with AI, this matters even more: it's far easier to regenerate with "large empty sky in the upper third" in the prompt than to retrofit space that isn't there.
Make yours
Everything here is built into the tools, and they are free to use: name your book, bring your manuscript or your artwork, and work as long as you like. You only pay when you want the files without the preview watermark.
Next: Typography and hierarchy · Back to What makes a cover sell