KDP Spine Width Calculator
Enter your page count and paper type. Your spine width appears instantly — in inches, millimetres and pixels at 300 DPI.
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Spine width
0.6756
inches
17.16
mm
203
px @ 300 DPI
0.6756 in — room for spine text.
The formula, explained
KDP builds paperbacks from two paper stocks, and each has a published per-page thickness: white is 0.002252 in per page, cream is 0.0025 in. Spine width is just multiplication:
spine width = page count × paper thickness
Worked example: a 300-page novel on white paper is 300 × 0.002252 = 0.6756 in — that's 17.16 mm, or 203 px at 300 DPI. Switch the same book to cream and it becomes 300 × 0.0025 = 0.75 in. Cream paper is about 11% thicker, which matters once you're deciding whether spine text will fit.
Spine widths at a glance
Every value below is computed from the same formula — 776 pages is the cream maximum, 828 the white maximum.
| Pages | White (in) | White (mm) | Cream (in) | Cream (mm) |
|---|---|---|---|---|
| 100 | 0.2252 | 5.72 | 0.25 | 6.35 |
| 150 | 0.3378 | 8.58 | 0.375 | 9.52 |
| 200 | 0.4504 | 11.44 | 0.5 | 12.70 |
| 250 | 0.563 | 14.30 | 0.625 | 15.88 |
| 300 | 0.6756 | 17.16 | 0.75 | 19.05 |
| 350 | 0.7882 | 20.02 | 0.875 | 22.22 |
| 400 | 0.9008 | 22.88 | 1 | 25.40 |
| 450 | 1.0134 | 25.74 | 1.125 | 28.57 |
| 500 | 1.126 | 28.60 | 1.25 | 31.75 |
| 550 | 1.2386 | 31.46 | 1.375 | 34.92 |
| 600 | 1.3512 | 34.32 | 1.5 | 38.10 |
| 650 | 1.4638 | 37.18 | 1.625 | 41.27 |
| 700 | 1.5764 | 40.04 | 1.75 | 44.45 |
| 750 | 1.689 | 42.90 | 1.875 | 47.63 |
| 800 | 1.8016 | 45.76 | — | — |
When can your spine carry text?
KDP's rule is firm: spine text is only printed on books with 79+ pages. Under that, your spine must stay blank — any text risks wrapping onto the front or back when the cover is folded.
Eligibility isn't the same as comfort. At 79 pages a white-paper spine is only 0.1779 in wide, and KDP also requires 0.0625 in of clearance between text and each fold. A practical rule of thumb: spines under about 0.25 in (roughly 111 pages on white paper) are too thin for comfortable spine text; from around 0.5 in you have room for a title and author name at a readable size.
Questions
Frequently asked questions
How accurate is this calculator?
It uses KDP's own published multipliers — 0.002252 in per page for white paper and 0.0025 in per page for cream — with no rounding until display. The result matches what KDP's cover calculator and template generator produce for the same inputs.
Which page count should I enter?
The final page count of your formatted interior PDF — the number KDP shows after you upload your manuscript, not your word-processor page count. Every page counts, including blanks, front matter and the copyright page.
Does trim size affect spine width?
No. Spine width depends only on page count and paper type. A 300-page book has the same 0.6756 in spine whether it is 5 × 8 in or 8.5 × 11 in. Trim size affects the overall cover width — see the cover size calculator for that.
Does this work for hardcovers?
No — KDP hardcovers use a different construction (case laminate with board and hinge allowances), so the math is different. This calculator is for KDP paperbacks only.