The calculation
outer sheet: front = last | 1, back = 2 | next-to-last
move inward by two page numbers per sheet
Worked example
An eight-page booklet has outer-sheet pairs 8 | 1 and 2 | 7, then inner-sheet pairs 6 | 3 and 4 | 5. A seven-page document uses the same arrangement with page 8 marked Blank.
Use this as a folding check
The table describes page pairs viewed upright on each face for a left-bound booklet. It is not a printer feed instruction. Short-edge versus long-edge duplex settings depend on page orientation, driver behavior and how the file is imposed. Print a numbered dummy before using your final artwork.
One signature at a time
For a book with several signatures, work on each group separately. The tool starts page numbering at one for the current group. Add the appropriate document offset when comparing later signatures with a full book. Do not nest every page of a long book into one group simply because the calculator accepts its page count.
The CSV lists both faces of every sheet so you can compare an imposition preview. It does not output a print-ready PDF, rotate artwork, account for right-to-left binding or compensate for paper creep. Those steps belong in the production file.
Common questions
Why is the first page next to the last page?
After the outer sheet is folded, those pages become the front and back of the booklet. Sequential pairs would not read in order.
Which duplex setting should I select?
Use your printer and software instructions, then test an eight-page numbered dummy. The page-pair map alone does not determine the correct feed orientation.
Further reading
Official or original references for the workflow; these organizations do not endorse this independent tool.