From Just Publishing Advice:
How well does your book thumbnail cover work? You might think that your cover image is fantastic. In a full-size view, it may well be.
But when it comes to book covers, the truism that people need to see something seven or eight times before they react is probably correct.
Readers looking for a new book to buy first have to notice, and then click, your thumbnail size cover to get to your buy page.
How does your tiny book cover image stack up for attracting attention-grabbing?
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Book thumbnail images are used on every book-related site you possibly think of, even on social media.
So it is vital that you consider your small image book cover size when you are making decisions about a new book cover. You need to pay attention to how your fonts and color choices look.
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Even the featured image of your book cover on your sales pages of Amazon, iBooks, Barnes & Noble, and other retailers are reduced to default thumbnails.
On Amazon, your book cover is reduced to approximately 500 x 333 pixels in the top left of your book sales page. To put this in perspective, an extremely low-resolution ebook cover is around 1280 x 720 pixels.
The best way to start analyzing how well your book cover works is to open your cover file in an image editor. Then reduce the size to create a thumbnail.
Thumbnails can be very small. Start with setting your dimensions to 90 pixels wide x 144 pixels tall.
Then view the actual size. You will see your cover in an approximation of an online thumbnail. You can experiment with additional image sizes.
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It is also important to remember that on top of reducing the dimensions, all sites reduce the image quality or resolution.
It is usually, at most, 72 dpi to make sure the file size is as small as possible.
If you can also change the resolution in your image editor, it will give you a better estimation of how good, or not, it will look online.
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Quoting Amazon’s recommendations regarding Kindle book cover size, the ideal size of ebook cover art is a height/width ratio of 1.6:1.
This means that for every 1,000 pixels in width, the image should be 1,600 pixels in height.
A cover 1280 pixels wide is generally the minimum size you should use. You can use jpg, gif, bmp, or png file types.
However, the full size of your custom image upload will never be seen online.
Your original uploaded image file will be reduced to a range of additional custom thumbnail image sizes.
Each one to suit different reading devices, on-screen applications, search engines, and different website use.
Amazon automatically generates a lot of different custom thumbnail sizes on its site.
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Here are a few examples to help you understand the necessity of covers that work in small dimensions.
On the Top Charts page, covers are quite small to give the chart number significance.
New releases are shown in the most common thumbnail medium view size, which is 107px x 160 px.
Recommendations are a little smaller at 90 px x 135 px.
Series books are usually a maximum of 135 px high.
In the You Viewed pane at the bottom of each book page, books that were viewed by people are squeezed into a 50 px x 50 px box.
That is insanely small.
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