How to test a book cover before you launch

BookBub tells advertisers to upload the cover image at 115 pixels wide, inside an ad unit that is 300 by 250 pixels. Amazon's KDP help pages call 2,560 pixels tall by 1,600 wide the ideal ebook cover. Those are the two ends of one file: you draw it at 1,600 pixels across, and a paying reader meets it at 115.

So the honest answer is that you cannot test a book cover at the size you made it. Every check worth running happens at the size and in the context a reader actually meets it. They go in a fixed order, each one has a stop condition, and nothing costs money until step four. Step four should usually not happen. I have shrunk every cover down to thumbnail before shipping it, for years, first by hand.

Run the checks in this order, and stop at the first failure

The order is the point. Each check is blunter and cheaper than the one after it, and each can kill the cover on its own, which means a cover that fails step one has not earned step two. Running them out of sequence is how an author ends up paying for a poll to settle a question the render already answered for free.

Read the last column first. A stop condition is not a warning you note and walk past. It means you go back to the file, change something, and start again at step one, because a change that fixes the 115-pixel render can break the lineup and a change that fixes the lineup can bury your title.

The order matters for a second reason too. The first three checks are free and take about an hour between them. The fourth costs money, and money spent on a poll is money not spent on the advertising that poll was supposed to protect.

Step one: shrink the cover to 115 pixels wide

Export a copy at 115 pixels wide and look at it at 100% on whatever monitor you own. Do not zoom in. Do not stare at the full-size file and imagine it smaller, which is the version of this check that everybody performs and nobody fails.

115 is not a round number chosen for effect. It is the width BookBub's own support page tells advertisers to use when uploading a cover into its creative builder, inside an ad unit of 300 by 250 pixels, and the same page warns that a very large upload gets reduced in a way that can hurt image quality. That is a retailer publishing the exact pixel width at which its paying subscribers see your book. "Thumbnail" is not a number. 115 is.

Set that against the file you built. KDP's ebook cover criteria page calls 2,560 pixels tall by 1,600 wide the ideal, puts the floor at 1,000 by 625, and asks for a height-to-width ratio of at least 1.6:1. Sixteen hundred pixels of width, rendered at 115. Divide it yourself: roughly fourteen to one across the width, and that reduction is the entire reason the rest of this sequence exists.

One fix falls straight out of the shrink and takes two minutes. If your cover has a white or very light background, Amazon's Cover Image Guidelines page suggests adding a narrow 3 to 4 pixel border in medium gray to define the boundaries of the cover. At 115 pixels the edges of a light cover dissolve into the page behind them and the book stops reading as an object at all. That border is the cheapest change in this whole post.

Save the shrunken file. You need it again at step two and at step three.

What you are looking for at 115 px is not detail. Detail is gone, and it is supposed to be gone. You are looking at silhouette, and at the value contrast between the dark parts and the light parts. Then you check whether the type is still a word or has gone to smear. I used to run this by carrying a printed proof to the far end of the studio and turning around. The export is faster and it is the same test.

What has to survive at that size, and what does not

At 115 pixels wide, exactly one element should survive, and you name which one before you shrink the file. A cover where the art, the title and the author name all stay legible at that size is not a well-tested cover. It is a cover with nothing in charge.

Name it first. Write the word on paper: figure, or title, or name, or the one shape. Then shrink the file and look at what your eye lands on before you can stop it. The test is whether you were right.

The other side of this is published by a retailer. Writing for Kobo Writing Life in 2016, designer JD Smith calls thumbnail legibility "one of the most overused phrases in publishing these days" and "one of the least understood," and states flatly that not everything on the cover has to be visible when your book is postage stamp size. I agree with that last sentence completely, which is exactly why the check above is not a legibility audit.

Here is the strongest case against me, the one a working designer makes in four seconds. Hierarchy is not elimination. Go look at the top twenty in romantasy or in thriller and you will find covers where the figure and the title both read at thumbnail, because the type was set large enough to carry and the art was kept simple enough to hold. That is craft, not failure. And for an author with real name recognition, the name is the asset; telling them to let it dissolve is malpractice.

The answer is that this is a prediction test, not a ban. Other elements are allowed to stay visible. They are not allowed to compete for first place. For a name-brand author the name is a perfectly legal choice of named element, because the requirement is that you chose one in advance, not that only one is present. So the failure is never "two things are visible." It is one of these:

• You could not predict which element would win, which means you do not know what the cover is selling.
• Two elements tie, and first place goes to whichever one a given reader's habits favor, which is a coin flip you are running on every impression.

Step two: stand it in a lineup of the books it competes with

Pull the top twenty in the exact Amazon category you intend to publish into, screenshot the grid, and paste your cover into a slot in the middle of the row at the same size as its neighbors. Then close the file and look at it cold the next morning. The question is not whether yours is the best cover in the row. It is whether a stranger scanning that row would sort yours into the same pile as the rest.

This is where "does it look good" stops being a useful question, because one manuscript can have a dozen correct covers. Celadon Books, which published Alex Michaelides's The Silent Patient on February 5, 2019 under ISBN 9781250301697, put twelve of that book's international covers side by side on its own site and says the novel is available in more than 40 territories. Same words inside, twelve different solutions outside, each one built for the shelf it was going onto. None of them is the objectively best cover. Each is the one that sorted correctly in its own market.

The lineup is only worth setting up when you have more than one candidate to drop into it, and that is the cheap half of the job: feeding the book description in for three drafts takes minutes, and choosing between them takes the morning.

Two failure patterns show up here more than anything else. The first is a cover that is better made than everything around it and reads as a different category, usually literary when the book is not. The second is a cover that matches the row so closely it vanishes into it, and that one hides, because it looks perfectly correct in isolation.

Stop here if your cover does not sort. Taking a cover that reads as the wrong genre to a paid poll buys you a precise measurement of the wrong thing.

Step three: ask three strangers one question, and not the obvious one

The obvious question is the useless one. Do not ask whether someone likes the cover, because liking is not what anybody buys on, and a preference answer tells you which of two strangers has better taste rather than anything about your book.

Ask this instead, of three people who know nothing about the manuscript. Show them the 115-pixel render, not the full-size file. Ask what kind of book they think it is, then ask what they think happens in it. Say nothing else. Do not name the genre, do not read the blurb, do not explain the symbolism, because every word you supply is a word the shelf will not.

Two of three naming the wrong genre is a stop condition. One of three is a shrug. Three of three is a cover for a different book than the one you wrote.

No published number backs this step, and I am not going to invent one. Three is a sample of three. What it catches is not a preference distribution, it is a category error, and category errors show up at n=3 precisely because they are not subtle.

Step four: when a $15 poll earns its money, and when it just buys you a tie

If you have two covers you would genuinely ship, a paid poll is worth its $15. If you have one cover and a nagging feeling, it is not, and it will hand you a number that feels like an answer.

PickFu is the tool most authors reach for at this step. Its pricing page puts responses at $1 each with a custom-designed poll starting at $15. Its help center lists fixed panel sizes of 15, 30, 50, 75, 100, 200, 300 and 500, calls 50 to 75 the sweet spot for actionable insight at a reasonable price, and says 15 responses can be plenty when the decision is between two clear options. Its book-cover page markets "results in minutes, not days." That is PickFu's claim about PickFu, and I am passing it on as such rather than confirming it.

I am not going to give you a margin of error, because PickFu does not publish one and I am not going to compute one off panel sizes. A narrow split and a wide split at the same panel size are not the same finding, and nothing on that page tells you where the line between them sits. Treat a close result as a tie, and go back to the file.

What a poll can settle, and what it cannot:

• Which of two covers a panel of strangers picks, given the exact question you asked them.
• Why they picked it, in their own words, which is the part actually worth the money.
• Whether the element you named at step one is the element they name back to you.
• It cannot tell you whether either cover sells, because nobody on that panel is buying anything.
• It cannot rescue a cover that failed step one or step two, because the panel will obligingly rank two versions of the same mistake.

Ask the poll the genre question, not the preference question. The comment field is where the money is.

What the whole sequence costs against what a launch costs

Add it up. Steps one, two and three cost nothing but about an hour, and step four starts at $15. Call the entire sequence $15 and a morning, and only if you get as far as step four at all.

Now the other column, all of it published. BookBub's partner pricing page lists a Featured Deal in Crime Fiction at $758 for a free book, rising to $3,566 at $3 and up, against a stated 2,240,000+ subscribers. BookBub's ads support page says a self-serve campaign can run on a budget of just $10, on a second-price auction where the winning bid pays the rate of the second-highest bid. Amazon Ads recommends a minimum of $10 per day per Sponsored Products campaign, notes that a single day can run 25% over that at $12.50, and says the month evens out around $300.

That is the comparison the whole post rests on. Fifteen dollars against $758, or against $300 a month, or against a $10 campaign you will keep feeding for as long as it looks like it is working. The cover is the thing all of that spend is buying attention for, and it is the last part of the machine you can still change for nothing.

What I will not tell you is how much more the tested cover sells. I went looking for an independent study measuring sales lift from cover A/B testing and could not find one I was willing to cite; every "3x conversion" figure I could trace ended at a vendor selling tests. So the argument here is cost asymmetry and nothing else. The checks are free or nearly free. The thing they protect is not.

What this sequence will not tell you

AthenaCover has no test step in it. What the product does between brief and file ends at the file: three cover variations with the title and author name set as real type, front cover only, no print wrap and no spine. It will not render one of them at 115 pixels, will not stand it beside your category's top twenty, and will not poll anyone. Every check in this post happens outside the product, in an image editor and a browser tab.

And step two is the one most likely to end with you not buying. If the two books yours would sit between in that row are hand-illustrated character covers with an illustrator credited on the jacket, generation is not going to get you there. Three free credits will not change that, and neither will the fourth. The lineup is the check whose honest output is sometimes "go hire a person," and I would rather you learned that before you spent anything than after.

The second thing this sequence cannot give you is the number everybody wants. Nobody can tell you what testing the cover was worth in sales, because the independent study does not exist. You are buying insurance at $15 against a launch budget you can look up.

The last check before you upload

Check the shortest side. KDP's Cover Image Guidelines says covers with less than 500 pixels on the shortest side are not displayed on the website, so a file that clears every check above can still show up as nothing. Apple Books wants at least 1,400 pixels on the shorter axis in RGB, and its asset guide rejects images enlarged from a smaller file. Export from the original, never from the 115-pixel copy.