A five-minute check at 100 pixels that catches the most common self-published cover problem before readers do.
1. The test
Open your cover in an image editor and resize the copy to 100 pixels wide, or step back from your screen until the cover is about the width of a thumbnail. You are checking one thing: can you read the title without knowing what it says? If you have to reconstruct the words from memory, the title is too small, too thin or too low-contrast.
2. What usually goes wrong
Three patterns show up again and again: a title set across a busy part of the image, an author name in a thin serif at small size, and a subtitle that crowds the title until both become one block. None of these require a new illustration; they require a type zone, more contrast and less text.
3. The fix that costs nothing
Move the type block into a quieter area and increase the size or weight one step at a time. Check the result at 100 pixels after each change. You are done when the title reads instantly and the author name is legible, not when the layout looks clever at full size.
4. When the artwork is the problem
If the subject and the type both need more space, the image is doing too much. Generate a direction with one subject and a reserved title zone instead of layering a second fix on top. That is a change worth making before you spend on ads, because a cover that reads at thumbnail size is the difference between a click and a scroll.
File sizes live in two places: the print cover measurements has the full wrap for each trim, and the calculator turns your page count and paper into the spine width.
cover measurements — A thumbnail is a crop of the front panel, so the cover measurements decide what survives the shrink.
What to do next
Open the free cover generator to test a direction, then run the cover size calculator for your trim and page count before you export. If the file still is not right, the design services page lists what a human pass covers. The guides index has the rest of the process in order.