Guide

KDP vs Lulu spine width

Publishing the same paperback on KDP and Lulu? The spine widths don't match, so neither does the cover. Here's how each platform calculates it.

Updated September 28, 2026

The formulas

KDP paperback

Spine width = page count × paper thickness:

White paper (black and white or standard color): 0.002252 in per page
Cream paper: 0.0025 in per page
Premium color: 0.002347 in per page

Lulu paperback

Spine width = (page count ÷ 444) + 0.06 in, whatever the paper. (Lulu's magazine and comic book paper uses 460 pages per inch instead of 444.)

Lulu hardcover

Lulu hardcovers don't use a formula. The spine comes from a fixed table in steps, for example 0.25 in for 24–84 pages and 1.25 in for 417–444 pages. See the full table in the Lulu spine width calculator.

Side-by-side spine widths

Pages	KDP white	KDP cream	Lulu paperback	Lulu hardcover
50	0.113 in	0.125 in	0.173 in	0.25 in
100	0.225 in	0.250 in	0.285 in	0.5 in
150	0.338 in	0.375 in	0.398 in	0.625 in
200	0.450 in	0.500 in	0.510 in	0.75 in
250	0.563 in	0.625 in	0.623 in	0.813 in
300	0.676 in	0.750 in	0.736 in	0.938 in
400	0.901 in	1.000 in	0.961 in	1.188 in
500	1.126 in	1.250 in	1.186 in	1.375 in
600	1.351 in	1.500 in	1.411 in	1.625 in
700	1.576 in	1.750 in	1.637 in	1.875 in
800	1.802 in	2.000 in	1.862 in	2.125 in

Other differences to watch

Safety margin: both need 0.125 in of bleed, but Lulu asks for text to stay 0.5 in inside the trim, while KDP's minimum is 0.125 in. A KDP cover with text near the edge can fail at Lulu.
Spine text: KDP allows it from 80 pages. Lulu advises against it at 80 pages or fewer.
Minimum pages: KDP paperbacks start at 24 pages, Lulu paperbacks at 32.
Trim names: the sizes often overlap (6 × 9 in is Lulu's "US Trade"), but Lulu has some KDP doesn't, such as 4.25 × 6.875 in Pocketbook.

Moving a cover from KDP to Lulu (or back)

Get the new full-cover size from the Lulu calculator or the KDP calculator.
Resize the canvas to the new width. The height stays the same for the same trim.
Keep the back cover anchored left, move the front cover right, and stretch or rebuild the spine to the new width.
Pull text in to the new safe margin (0.5 in for Lulu).
Check the result with the cover checker, which supports both platforms.

Frequently asked questions

Can I use the same cover file on KDP and Lulu?

Usually not. The spine widths differ, so the full cover width differs too: a 300-page 6 × 9 in paperback needs 12.926 in on KDP (white paper) but 12.986 in on Lulu. Resize the canvas and move the front cover so the spine lines up.

Which is wider, a KDP or a Lulu spine?

Lulu’s 444 pages per inch works out to the same thickness per page as KDP white paper (0.002252 in), so a Lulu paperback spine is always exactly 0.06 in wider than a KDP white-paper spine. KDP cream paper is thicker per page, so above about 242 pages a KDP cream spine is wider than Lulu’s.