How We Calculate: Formulas & Assumptions

spine = page count × paper factor. Factors are the per-page values published by Amazon KDP. For printers that specify pages per inch, spine = page count ÷ PPI.

cover width = 2 × trim width + spine + 2 × bleed, cover height = trim height + 2 × bleed, with 0.125 in bleed unless stated.

Text area = trim minus margins (inside margin = platform minimum for the page count + 0.25 in; outside 0.5–0.75 in; top and bottom 0.625–0.75 in) minus 0.3 in for running heads and folios. Lines = text height ÷ (type size × 1.3). Characters per line = text width ÷ (type size × 0.46). Words per line = characters ÷ 6. A fill factor of 0.82 (fiction) or 0.9 (nonfiction) accounts for paragraph ends, dialogue and breaks.

Page count = words ÷ words per page + 0.6 page per chapter (one chapter per 3,500 words of fiction or 5,000 of nonfiction) + 10–12 pages of front and back matter, rounded up to an even number. Typical accuracy is ±10–15%.

Weight = leaves × trim area × paper grammage + cover area × 250 g/m². Reading time uses 238 words per minute, the average silent reading rate for adults in English found by Brysbaert (2019). Audiobook length uses 9,300 words per finished hour (about 155 words per minute).

Minimum inside margins by page count are KDP's published values: 0.375 in (24–150 pages), 0.5 in (151–300), 0.625 in (301–500), 0.75 in (501–700) and 0.875 in (701–828).

Signature layouts are computed by simulating right-angle folds of a numbered sheet; the last fold forms the spine. Printers may use mirrored or rotated equivalents.