How many A4 sheets do you need for a poster?
Four for A2, eight for A1, sixteen for A0 — but only if you turn the sheets sideways at every second step. Here is the whole table, and the two things that push the real number above it.
The short answer
These are the counts for tiling edge to edge, with no overlap and nothing wasted. They are the floor: the number you cannot go below, whatever tool you use to get there.
| Poster | Size | A4 sheets | Grid | How the sheets go in |
|---|---|---|---|---|
| A3 | 297 × 420 mm | 2 | 1 × 2 | Sideways (landscape), one above the other. |
| A2 | 420 × 594 mm | 4 | 2 × 2 | Upright, exactly as the paper comes out of the tray. Fits to the millimetre. |
| A1 | 594 × 841 mm | 8 | 2 × 4 | Sideways again. This is the row everyone gets wrong — see below. |
| A0 | 841 × 1189 mm | 16 | 4 × 4 | Upright. Lands within a millimetre of true A0. |
Why A1 is eight sheets and not nine
Every step down the A series halves the sheet and swaps its proportions round: A3 is a wide A4, A2 is a tall A3, and so on. Two steps therefore bring you back to the shape you started with. That is why A2 and A0 tile so neatly — A4 to A2 is two steps, so four upright sheets in a 2 × 2 grid measure 420 × 594 mm, which is A2 to the millimetre, and sixteen in a 4 × 4 grid land on A0 the same way.
A1 is three steps from A4, so its proportions are transposed. Keep every sheet upright and nothing fits: you need three columns to cover 594 mm of width, and they give you 630. You need three rows to cover 841 mm of height, and they give you 891. That is nine sheets, with a 36 mm strip wasted down one side and a 50 mm strip along the bottom.
Turn every sheet sideways instead and two columns cover 594 mm exactly, four rows cover 840 mm, and eight sheets do the job with nothing thrown away. The nine you see quoted everywhere is simply what happens when nobody rotates the paper.
What the overlap costs you
Overlapping the sheets makes them far easier to line up, but it is not free: every sheet gives up a strip along each edge it shares with a neighbour, so it covers less poster than its full size suggests.
The effect is bigger than people expect on small posters. With a 5 mm overlap an A2 no longer fits in four sheets — each upright sheet now contributes 205 mm of width instead of 210, so 420 mm needs three columns rather than two. The Poster tool works around it by turning the paper sideways and printing eight, which is the smallest grid that still covers the poster at that overlap.
As a rule, an overlap adds roughly one row and one column once a poster is more than a couple of sheets across. If the sheet count matters more to you than the ease of assembly, set the overlap to zero, trim exactly on the cut line and butt the sheets together instead.
The strip every sheet loses
PrintReal reserves 10 mm at the top of every sheet for the tile label and the small assembly map — the things that make a stack of twelve near-identical pages sortable after it leaves the printer. That band is why an A2 comes out as six sheets rather than four even with the overlap set to zero: each sheet contributes 287 mm of height instead of 297.
Home printers take their own cut as well. Almost none of them print to the edge of the paper; a margin of about 5 mm on each side is normal, and it is unprintable whatever the file says. So read the table above as the floor rather than the forecast — for A2 on A4 the honest range is four sheets in theory, six with the label band, and eight once you add an overlap you can actually work with.
Poster sizes in inches
Letter paper is not part of the ISO series and its proportions are nothing like the √2 the A sizes are built on, so these never tile exactly the way A-series posters do. There is always some waste; the grids below are the smallest ones that cover each poster.
| Poster | Size | Letter sheets | Grid | How the sheets go in |
|---|---|---|---|---|
| Tabloid | 279 × 432 mm | 2 | 1 × 2 | 11 × 17 in, and exactly two Letter sheets with nothing wasted. Sideways, one above the other. |
| 18 × 24 in | 457 × 610 mm | 6 | 2 × 3 | Sideways. The area is only 4.6 sheets; six is the smallest grid that covers it. |
| 24 × 36 in | 610 × 914 mm | 12 | 3 × 4 | Upright. The standard film-poster size, and the one worth checking your ink level for. |
Working it out for any size
Divide, do not multiply. Comparing areas gives you the theoretical minimum and almost never the real answer, because sheets cannot be cut into fractions and laid into the gaps.
Take the poster width, divide it by the usable width of one sheet and round up — that is your number of columns. Do the same with the height for the rows, then multiply the two. The usable width is the sheet width minus the overlap; the usable height is the sheet height minus the overlap and minus the 10 mm label band.
For a poster 700 mm wide on upright A4 with a 5 mm overlap: 700 ÷ 205 is 3.4, so four columns. If it is 1000 mm tall, 1000 ÷ 282 is 3.5, so four rows. Sixteen sheets. Then run the same sum with the paper sideways — for most poster shapes one of the two orientations needs noticeably fewer sheets, and it is not always the one that matches the poster.