Cover geometry: spine width and the full wrap

KDP does not take three files. It takes one flat image containing the back cover, the spine and the front cover, laid out left to right, with bleed all round.

Spine width

Spine width is page count multiplied by paper thickness:

A 240-page book on white paper:

240 x 0.002252 = 0.5405 in

Cream paper is thicker. The same book on cream is 0.6 in — a difference of nearly 1.5 mm, which is enough to shift your spine text visibly off centre.

The full cover

width  = 0.125 + back + spine + front + 0.125
height = trim height + 0.25

For that 240-page 6 x 9 book on white paper:

width  = 0.125 + 6 + 0.5405 + 6 + 0.125 = 12.7905 in
height = 9 + 0.25 = 9.25 in

At 300 DPI that is 3837 x 2775 pixels. Build at that exact size. Scaling a cover up afterwards is how a crisp title turns soft.

Spine text has rules

Under 100 pages, do not put text on the spine at all. The spine is too narrow for the printing tolerance and KDP will reject it.

Above 100 pages, keep spine text at least 0.0625 in clear of both spine edges. Printing shifts by up to about 0.0625 in in either direction — that is normal, not a defect. A title that exactly fills the spine will look crooked on some copies of the same print run.

The same tolerance applies to the front. Keep anything that must not be cut at least 0.25 in inside the trim line, and never put a thin border right at the edge: a 2 mm shift turns an even frame into an obviously uneven one.

Export settings

• PDF or a 300 DPI JPEG/TIFF, in CMYK. An RGB cover will be converted, and bright RGB blues and greens go dull.
• No transparency, no layers. Flatten it.
• No spot colours.

Before the next lesson

Build the cover at the exact calculated size and open KDP's previewer before you do anything else. It shows the real trim line over your artwork, and it is the only place you find out that your subtitle is 3 mm from being cut in half.