You entered your size, and the app wants 15 sheets where you expected 12. Or you raised the margin and a whole extra column appeared.
Nothing is wrong. Two rules explain almost every case.
Rule 1 — the count uses the usable area, not the sheet
Each sheet loses its margin to the blank band around the edge. The sheet count is computed against what is left:
columns = round up ( poster width / ( paper width - margins ) )
rows = round up ( poster height / ( paper height - margins ) )So at a 0.50 in margin, an A4 sheet contributes noticeably less than an A4's worth of poster. Raise the margin to 0.75 in and it contributes less still — which is why raising the margin can add a whole row or column.
Rule 2 — it always rounds up
A poster one millimetre wider than a whole number of sheets costs a complete extra column. There is no partial sheet.
This is why a size like 60.2 cm can cost the same as 75 cm. Try nudging the dimension down slightly and watch the count.
What to change
| Try | Effect |
|---|---|
| A larger paper size | The most effective single change. A3 is twice the area of A4, so it roughly halves the sheet count. |
| Reduce the margin | 0.75 to 0.50 in recovers usable area. Do not go below 0.50 without reason — see cropped pages. |
| Adjust the poster size slightly | A centimetre either way can drop a column, because of the rounding. |
| Switch orientation | A landscape poster on portrait sheets often tiles worse than the reverse. |
| Switch to grid mode | If the exact size does not matter, choose the sheet count and let the size follow. |
"Grid auto-adjusted for margins"
If the app shows this note, the grid drawn on the canvas and the number of sheets the export produces are not the same. That is expected: the canvas grid shows your layout, and the export count is recomputed against the usable area with your margin applied.
Trust the export count — that is how many sheets will come out of the printer. It is explained in full in grid mode and size mode.
Check the count before you print
The export preview shows the page count. It updates as you change the margin, the paper size and the dimensions, so you can find a good combination before committing paper and ink to it.