A book cover’s job isn’t to be beautiful in the abstract. It’s to be instantly readable at thumbnail size and to signal genre correctly within a couple of seconds, because that’s the format almost every reader encounters it in first. A gorgeous cover that fails at 150 pixels wide has failed at the one job that matters most.

The Thumbnail Test

Around 70% of book discovery happens on mobile devices, at thumbnail size, a small rectangle competing with dozens of others for a moment of attention. Design at full size and check the thumbnail last, and you’ll routinely end up with a title that vanishes, a focal point that turns to noise, or text that reads as a grey smudge at small size.

Design at thumbnail size first instead. If the title isn’t legible around 100 to 150 pixels wide, no amount of detail at full size fixes that, because almost nobody sees your cover at full size before they’ve already decided whether to look closer.

Genre Conventions

Readers use cover cues as shorthand before they’ve read a single word of your description. Breaking genre convention is possible and sometimes effective, but it’s a deliberate choice made after you understand what you’re breaking, not an accident from not knowing the convention existed.

Romance: warm tones, often illustrated or photographic figures, script or elegant serif typography.

Thriller and mystery: high contrast, dark backgrounds, bold sans-serif typography.

Fantasy: saturated colour, textured or illustrated depth, typography that can range from classic serif to more stylised display fonts depending on subgenre.

Literary fiction: more restrained, often a single strong image or abstract composition, classic serif typography that signals a different kind of read than commercial genre fiction.

These are starting points, not rules with no exceptions, but a cover that ignores its genre’s visual language entirely is asking a browsing reader to do work they have no reason to do, when dozens of other covers in the same feed are already speaking that language clearly.

Typography Rules

Maximum two fonts. One for the title, a complementary second font for the author name and any subtitle. More than that reads as amateur.

Legible at thumbnail size, non-negotiably. Thin, delicate fonts and highly decorative scripts are the first thing to fail this test. If you love a font but it disappears at small size, it can’t be the title font, however good it looks at full resolution.

Genre-appropriate weight and style. A thin, elegant script on a thriller, or heavy distressed lettering on a literary novel, sends a genre signal that fights against the book itself.

Contrast matters as much as font choice. Title text needs to separate cleanly from whatever’s behind it. A technically nice font in a colour too close to its background fails the same way a bad font choice does.

DIY or Custom

Premade or template-based covers (Canva, marketplace templates, a designer’s existing catalogue with your title dropped in) are a legitimate choice, not just a budget compromise, particularly in genres with strong, consistent visual conventions a template can satisfy well. The full cost breakdown for both routes is in what self-publishing costs.

Custom design gives you a cover built specifically around your book’s actual content and comp titles, worth it once you have a clearer sense of exactly what needs to be on the cover to represent the story honestly.

Neither path is inherently the wrong choice. A well-chosen premade cover in a genre with tight conventions can outperform a mediocre custom one. A distinctive or cross-genre book is harder to represent with an off-the-shelf template, and needs the custom route to represent it accurately.

Research Before You Design

Before choosing anything, screenshot twenty to thirty bestselling or well-regarded covers in your specific genre and subgenre. Look for patterns: colour palettes, typography styles, common imagery, layout conventions. This is about understanding what visual language your readers already associate with the kind of book you’ve written, not about copying a specific cover, so your cover speaks that language even if the specific execution is entirely your own.

Technical Specs for KDP

Ebook cover: minimum 1,000 pixels on the longest side, an exact 1.6:1 aspect ratio, RGB colour mode, saved as JPG or TIFF.

Print cover: a single wraparound file, back cover, spine, and front cover combined, with spine width calculated from your final page count. 300 DPI minimum, CMYK colour mode rather than RGB, and 0.125 inches of bleed beyond the trim edge wherever the design reaches the edge of the page.

Getting these specs wrong doesn’t just look unprofessional, it can cause an upload to be rejected outright, so it’s worth checking against KDP’s current requirements at the point you’re ready to upload, not relying on specs from a guide written months earlier.

Writing Desk tip: The Formatter handles your manuscript’s interior typesetting, front matter, chapter openers, page numbers, so once your cover is finalised, the interior can be styled to feel like it belongs with it rather than looking like two separate projects bolted together.

Final Words

A cover’s job is narrow and specific: pass the thumbnail test, signal genre correctly, and hold up against the twenty or thirty covers already doing that well in your category. Everything else, personal taste, artistic ambition, how much you personally love a particular font, matters less than those three things working.

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