The thumbnail test
Here is the uncomfortable arithmetic. A 6 × 9 front cover with bleed is 1,838 × 2,775 pixels at 300 DPI — the file you have been staring at, zoomed to fill a screen. In a phone's search results it is shown at about 100 to 160 pixels tall: roughly a postage stamp, a seventeenth of its height, and nearer a three-hundredth of its area.
Almost every purchasing decision starts there. The full-size cover is what a reader sees after they've decided to look closer, and most never do.
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. Press Cover check…. It renders your finished front — artwork, title and all, not the raw art — at about 160 px for a search result and 100 px for a recommendation strip, beside a grayscale panel for the value-contrast problem below. Start your cover → · 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 to about 1.5 cm / half an inch tall — on a laptop, roughly 160 pixels.
- Look at it from normal reading distance. Don't lean in.
- 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 — and Genre conventions: what your cover has to promise is the vocabulary to check yourself against.
Does one thing dominate? Or does it dissolve into visual soup? Some objects survive being shrunk and some turn to mush: Objects and symbols that read at thumbnail size.
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. This is how readers meet your book — never alone, always in competition — and covers that look fine alone disappear in a grid. Show it to readers of your genre rather than to yourself and it gets harder again: Testing a cover with readers.
The grayscale test. Desaturate the thumbnail. If the title vanished when the color left, you were relying on hue contrast rather than value contrast — a common and expensive mistake: Color and contrast. It doubles as a print check, because ink on uncoated stock lands flatter and darker than a backlit screen (Why your cover prints darker than it looked).
What usually fails
The title is too small. By far the most common. At full size a modest title looks restrained; at thumbnail it's gone. Professional covers run type far bigger than feels comfortable when you're zoomed in, with the title carrying most of the 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. Design that space from the start rather than hunting for a gap afterwards — Composition and negative space.
Thin lettering, and the effects propping it up. Hairline serifs, script faces and ornamented display type lose their strokes when shrunk, and the drop shadows, glows and outlines holding them together measure a few pixels at design size — less than one at thumbnail. A long title makes it worse, because the instinctive fix is to shrink it: Setting a long title without shrinking it.
The author name competing with the title. At full size a big name reads as confidence. At 160 px, two lines of similar-weight type are one block of noise. Unless your name sells the book, put it clearly second — Typography and hierarchy.
Too many elements, too little contrast. Four things at full size is cluttered; four at thumbnail is a gray smudge. And pale type on a pale sky reads at 1,838 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.
Follow that logic far enough and you reach Covers made of nothing but type, the most reliable thumbnail on any shelf: no image in the way, nothing left to compete with the title.
What the test does not tell you
Passing is necessary, not sufficient. It is blind to three things.
Everything that only shows up large. Misaligned type, uneven spacing and an optically off-center title vanish at 160 px and are glaring on a product page and on the printed book — Alignment, spacing and why an amateur cover feels off.
Whether the file will print. A screenshot at 160 px looks immaculate whatever the source resolution. The Cover Maker flags artwork under 200 DPI at its printed size for exactly that reason; Resolution: why a good-looking image prints badly explains the number.
The other shapes your cover takes. A 6 × 9 front is 1:1.5; the ebook cover is 1600 × 2560, or 1:1.6, so cropping to it loses about 6% of the width, 3% from each side, and type near a vertical edge can pass in print and fail as an ebook. Test that crop too (Ebook cover size, and why it is not your print front), and any ad image, where the rules apply smaller still: What goes in a book ad.
Do this before you finish, not after
Run this at the sketch stage, when changing the composition costs nothing. Most authors run it at the end 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.
With AI artwork it matters more, not less: 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. AI cover art that does not look like AI cover art covers the rest of that workflow.
Make your cover
The Cover Maker is free to use: name your book, bring your artwork, and it draws the full wrap — front, spine and back — to your printer's own measurements. You only pay when you want the files without the preview watermark.
Next: Typography and hierarchy · More: What makes a book cover sell · Objects and symbols that read at thumbnail size · Testing a cover with readers