acalculator

How big should my book cover be?

Type your book’s trim size, page count and paper. The KDP cover calculator works out the spine width and the full wraparound cover (back, spine and front with a 0.125 in bleed) by Amazon KDP’s published formulas, in inches and millimeters.

Your numbers

Units
Full cover width (in)
12.926

The full cover is 12.926 in wide and 9.25 in high, with a 0.676 in spine.

Full cover height (in)
9.25
Spine width (in)
0.676
Full cover width (mm)
328.31
Full cover height (mm)
234.95
Spine width (mm)
17.16
Spine text
Allowed (79 pages or more)
Spine text area width (in)
0.551

Full cover width (in): 12.926. The full cover is 12.926 in wide and 9.25 in high, with a 0.676 in spine.

How to calculate

Works out the full wraparound cover size and spine width of a print-on-demand paperback from its trim size, page count and paper, by the Amazon KDP formulas with a 0.125 in bleed.

Example with the default inputs (Trim width 6 in, Trim height 9 in, Page count 300, Ink and paper Black ink, white paper): The full cover is 12.926 in wide and 9.25 in high, with a 0.676 in spine.

Method: spine = pages × thickness (0.002252 in white or standard color, 0.0025 in cream, 0.00235 in groundwood, 0.002347 in premium color); width = 0.125 + trim width + spine + trim width + 0.125; height = 0.125 + trim height + 0.125.

  • A paperback with a 0.125 in (3.175 mm) bleed on every outside edge, as KDP asks for.
  • Page count ranges are KDP’s for most trim sizes; large trims such as 8.5 × 11 in allow fewer pages.
  • Typed sizes are read exactly, so sizes typed in millimeters convert exactly (1 in = 25.4 mm).
  • Check KDP’s own cover template before you upload; KDP may change its paper thicknesses.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Trim width 6 in, Trim height 9 in, Page count 300, Ink and paper Black ink, white paper gives Spine width (in) 0.6756, Full cover width (in) 12.9256, Full cover height (in) 9.25, Spine text Allowed (79 pages or more), Spine text area width (in) 0.5506.Source: Amazon KDP Help, Create a Paperback Cover (spine width = page count × 0.002252 in for white paper, 0.0025 in for cream, 0.002347 in for premium color, 0.002252 in for standard color; cover width = bleed + back + spine + front + bleed; bleed 0.125 in; spine text needs at least 79 pages and 0.0625 in from each spine edge), https://kdp.amazon.com/en_US/help/topic/G201953020 (retrieved 2026-10-02)
  2. Trim width 5.5 in, Trim height 8.5 in, Page count 200, Ink and paper Black ink, cream paper gives Spine width (in) 0.5, Full cover width (in) 11.75, Full cover height (in) 8.75, Full cover width (mm) 298.45.Source: Amazon KDP Help, Create a Paperback Cover (spine width = page count × 0.002252 in for white paper, 0.0025 in for cream, 0.002347 in for premium color, 0.002252 in for standard color; cover width = bleed + back + spine + front + bleed; bleed 0.125 in; spine text needs at least 79 pages and 0.0625 in from each spine edge), https://kdp.amazon.com/en_US/help/topic/G201953020 (retrieved 2026-10-02)
  3. Trim width 8.5 in, Trim height 11 in, Page count 60, Ink and paper Premium color, white paper gives Spine width (in) 0.14082, Full cover width (in) 17.39082, Spine text Not allowed (under 79 pages).Source: Amazon KDP Help, Create a Paperback Cover (spine width = page count × 0.002252 in for white paper, 0.0025 in for cream, 0.002347 in for premium color, 0.002252 in for standard color; cover width = bleed + back + spine + front + bleed; bleed 0.125 in; spine text needs at least 79 pages and 0.0625 in from each spine edge), https://kdp.amazon.com/en_US/help/topic/G201953020 (retrieved 2026-10-02)
  4. Trim width 6 in, Trim height 9 in, Page count 400, Ink and paper Black ink, groundwood paper gives Spine width (in) 0.94, Full cover width (in) 13.19.Source: Amazon KDP Help, Paperback Submission Guidelines (groundwood paper: page count × 0.00235 in), https://kdp.amazon.com/help?topicId=G201857950 (retrieved 2026-10-02); Amazon KDP Help, Set Trim Size, Bleed, and Margins (page counts 24 to 828 white, 24 to 776 cream, 24 to 812 groundwood, 72 to 600 standard color, 24 to 828 premium color for most trim sizes; bleed 0.125 in), https://kdp.amazon.com/en_US/help/topic/GVBQ3CMEQW3W2VL6 (retrieved 2026-10-02)

How it works

Everything is worked out in inches, from KDP’s published formulas:

  • spine width = page count × thickness per page: 0.002252 in (white paper, and standard color), 0.0025 in (cream), 0.00235 in (groundwood), 0.002347 in (premium color)
  • full cover width = 0.125 + trim width + spine + trim width + 0.125
  • full cover height = 0.125 + trim height + 0.125
  • spine text is allowed when the page count is at least 79; the spine text area is the spine width − 2 × 0.0625 in
  • millimeters = inches × 25.4

The trim width and height can be typed in inches, millimeters or centimeters. Each is read as the exact decimal you typed in its unit (1 in = 25.4 mm exactly), so the sizes are exact and are rounded once, halves up.

Rules

  • Trim width and height are from 2 in to 20 in (50.8 mm to 508 mm).
  • The page count is a whole number in KDP’s range for the paper: 24 to 828 for white and premium color, 24 to 776 for cream, 24 to 812 for groundwood, and 72 to 600 for standard color. A count outside the range has no answer.

Output format. Inches to 3 decimal places and millimeters to 2. Spine text as "Allowed (79 pages or more)" or "Not allowed (under 79 pages)"; the text area only when it is allowed.

Worked examples by hand

6 × 9 in, 300 pages, white paper. Spine = 300 × 0.002252 = 0.6756 in. Width = 0.125 + 6 + 0.6756 + 6 + 0.125 = 12.9256 in (12.926 shown); height = 9.25 in. Spine text allowed; text area 0.6756 − 0.125 = 0.5506 in.

5.5 × 8.5 in, 200 pages, cream paper. Spine = 200 × 0.0025 = 0.5 in. Width = 0.25 + 11 + 0.5 = 11.75 in = 11.75 × 25.4 = 298.45 mm; height 8.75 in.

8.5 × 11 in, 60 pages, premium color. Spine = 60 × 0.002347 = 0.14082 in; width = 0.25 + 17 + 0.14082 = 17.39082 in. Under 79 pages, so no spine text.

6 × 9 in, 400 pages, groundwood. Spine = 400 × 0.00235 = 0.94 in; width = 0.25 + 12 + 0.94 = 13.19 in.

Other questions people ask

How do I calculate the spine width of a paperback?

Multiply the page count by the thickness of one page. KDP gives 0.002252 in per page for white paper, 0.0025 in for cream, 0.00235 in for groundwood, 0.002347 in for premium color and 0.002252 in for standard color. A 300 page book on white paper has a 300 × 0.002252 = 0.6756 in spine.

How wide is the full cover?

The cover is one image of the back, the spine and the front, plus a 0.125 in bleed on the outside edges: width = 0.125 + trim width + spine + trim width + 0.125. For a 6 × 9 in book with a 0.6756 in spine that is 12.9256 in, and the height is 9 + 0.25 = 9.25 in.

Can I put text on the spine?

Only if the book has at least 79 pages. Below that the spine is too thin and KDP rejects spine text. Keep the text at least 0.0625 in (1.6 mm) from each spine edge, so the calculator also shows the spine width minus 0.125 in.

Why does the paper type change the cover size?

Each paper has a different thickness, so the same page count makes a different spine. 200 pages is a 0.4504 in spine on white paper but 0.5 in on cream, and the full cover grows by the same amount.

What is bleed?

Bleed is extra artwork past the trim line, so the printed color reaches the edge after the book is cut. KDP asks for 0.125 in (3.2 mm) on the top, bottom and outside edges of the cover. Keep text and important art away from the trim line.

Does this work for hardcovers?

No. Hardcover cases wrap around boards and use other sizes. This calculator follows the paperback cover rules only.