Why the pages are in the wrong order
Take the staples out of any booklet and the pages are not in order. They are not meant to be.
6min read · Craft
Take a stapled booklet and open the staples. The sheets fall apart in your hands, and what you are holding looks like a mistake. The first sheet does not carry pages 1 and 2 side by side. It carries the first page and the last page together, and the second and second-to-last on the back. Printers call this imposition, and once you see the rule it stops being mysterious.
One sheet, four pages
Start with the smallest case. Take one sheet of A4, print on both sides, and fold it in half so it becomes an A5 booklet of four pages. Number the pages as a reader would meet them: the front cover is 1, the inside left is 2, the inside right is 3, and the back cover is 4.
Unfold the sheet and look at the outside. The back cover and the front cover sit next to each other, 4 on the left and 1 on the right. Turn it over and the inside shows 2 on the left and 3 on the right. So the sheet front reads 4 | 1 and the sheet back reads 2 | 3. Nobody printing a file of four pages in reading order would get that without help.
Why the outside pairs the first with the last
The reason is geometry. The outside of a folded sheet is the cover and the back cover, and the two are physically the two ends of the book. Anything that sits at the very start sits next to the very end on the flat sheet. The same logic repeats inwards: the second page shares a sheet side with the second-to-last, because they are the next two ends once you remove the cover.
For a booklet of any length that is a multiple of four, the rule is this. List the pages. Take one from each end and pair them: last with first, second with second-to-last, and so on. Each sheet side carries one such pair, and each sheet carries two sides. Move inwards by one pair per side as you go from the outermost sheet to the innermost.
Eight pages as an example
For eight pages saddle stitched, the outer sheet holds 8 | 1 on the front and 2 | 7 on the back. The inner sheet holds 6 | 3 on the front and 4 | 5 on the back. Nest the inner sheet inside the outer sheet, staple through the fold, and the pages read 1 to 8 in order.
The Folding Table on this site shows that exact layout with a toggle between sheets, so you can see which pair goes where. Switch to sixteen pages and you will see four sheets and the pairs shifting inwards in the same pattern.
Why some numbers are upside down
If you print on both sides of a sheet, the printer has to flip the sheet over to print the second side. How it flips matters. Flip on the long edge and the back lines up with the front as you would turn a page in a book. Flip on the short edge and the back appears upside down relative to the front, as if you turned a calendar page.
For a booklet that is folded across the middle of a landscape sheet, the two panels on the back can end up rotated 180 degrees when the flip is on the short edge. That is why the table draws a triangle on some panels. It is not an error. It tells you which pages the printer will print inverted so that after the physical flip they come out the right way up.
In practice most office printers have a setting called something like “flip on long edge” or “flip on short edge”. If the back of your test print looks upside down, you have chosen the wrong one for your layout, and the fix is to change the flip setting, not to rearrange the pages.
Padding to a multiple of four
One more rule explains the page counts. A sheet folded once has four pages, so a saddle-stitched booklet always has a count that is a multiple of four. If you have fourteen pages of content, you need sixteen. The extra two are blank. Where do they go? The usual choice is the end, so the booklet closes on a blank inside back cover, though many people use the spare page for a note, a colophon or an advert.
Put the blanks at the back unless you have a reason not to. If you need a blank at the front (say, a half-title page), plan for it deliberately and count it as page content, not padding.
A mock-up is faster than a theory
You can check any layout with scrap paper in under two minutes. Fold the right number of sheets, nest them, and number every page by hand in reading order, writing small. Unfold each sheet and compare it with the diagram. If a number is upside down on your paper but not on the diagram, or the other way round, the flip edge is the thing to inspect.
If the result looks like a puzzle, remember that it is solving a real constraint: one flat sheet must become several pages without cutting. The strange order is just the shortest path from flat paper to a book.
What to do next
Decide your page count first. Round up to a multiple of four. Choose the finished page size and the sheet it will be cut from, then look at the layout in the table. When you send files to a print shop, tell them whether you are supplying pages in reading order, which is the normal request, or already imposed sheets. Most shops prefer reading order and will impose them for you. The table’s print-shop note covers that conversation so you can paste it into an email.