How many sheets a poster takes
A home printer cannot print to the edge, so what counts is the printable area. This page assumes a margin of 0.25 inch on every side; check your printer's minimum and adjust. A Letter sheet then has 8 × 10.5 inches of printable area, an A4 sheet about 7.8 × 11.2 inches.
Do it for width and height, multiply, and try both sheet orientations. The table picks whichever needs fewer sheets. The middle column adds a 0.5-inch overlap between neighbors, using round up ((side − overlap) ÷ (printable − overlap)).
| Poster | Letter | Letter, 0.5 in overlap | A4 |
|---|---|---|---|
| 18 × 24 in | 2 × 3 = 6 | 2 × 4 = 8 | 2 × 4 = 8 |
| 24 × 36 in | 3 × 4 = 12 | 3 × 5 = 15 | 3 × 5 = 15 |
| A2 | 2 × 3 = 6 | 2 × 4 = 8 | 2 × 4 = 8 |
| A1 | 3 × 4 = 12 | 3 × 5 = 15 | 4 × 3 = 12 |
| A0 | 4 × 6 = 24 | 5 × 5 = 25 | 3 × 7 = 21 |
Columns come first, then rows. The A sizes come from ISO 216: every sheet in the series has the same 1 to square root of 2 proportions, A0 has an area of one square metre, and each next size is half of the one before. The guide A4 vs Letter lists all of them with US sizes.
A worked example: 24 × 36 inches on Letter
A 24 × 36 inch poster on Letter paper in portrait: 24 ÷ 8 = 3 columns and 36 ÷ 10.5 = 3.4, rounded up to 4 rows. That is 12 sheets. Split evenly, each tile covers 8.0 × 9.0 inches of the poster, which fits inside the 8 × 10.5 inch printable area with a little room to spare.
Now the pixels. Suppose the image is 4,000 × 6,000 pixels. Across 24 inches that is 167 pixels per inch, and each of the 12 tiles gets 1,333 × 1,500 pixels. Print each tile at exactly 8.0 × 9.0 inches and the pieces add up to the full poster.
How many pixels the image needs
Pixels needed = inches × pixels per inch, for each side. The design service of the US Government Publishing Office asks for photos at 300 dpi. A poster seen from a few steps away is usually printed at less; the table gives both 300 and 150 ppi.
| Poster | At 300 ppi | At 150 ppi |
|---|---|---|
| 18 × 24 in | 5,400 × 7,200 | 2,700 × 3,600 |
| 24 × 36 in | 7,200 × 10,800 | 3,600 × 5,400 |
| A2 | 4,961 × 7,016 | 2,480 × 3,508 |
| A1 | 7,016 × 9,933 | 3,508 × 4,967 |
| A0 | 9,933 × 14,043 | 4,967 × 7,022 |
To check what your image will deliver, the PPI calculator takes a resolution and a diagonal; enter the poster's diagonal instead of a screen's. The image resizer can scale an image to exact pixel dimensions, for example to make its sides divide evenly by the grid. Resizing up does not add detail, though. GPO also warns that images taken from the web have too little resolution for print.
Split the image into tiles
The image splitter cuts a picture into a grid of equal tiles, up to 10 columns and 10 rows, and downloads them as a numbered ZIP. Tile 1 is the top left one. Choose the grid from the table above, keep the image's own shape, and leave the gap setting at 0 so no pixels are skipped between tiles. Each tile keeps the original pixels of its part of the image unless you set a tile width.
The splitter does not add overlap: neighboring tiles meet edge to edge. That is fine, because the white printer margin does the job instead, as the next section shows.
Print and join the sheets
- Print at actual size. In the print dialog choose 100 percent or actual size, not fit to page, and set the image size to the tile size, 8.0 × 9.0 inches in the example. Use the same settings for every tile.
- Number the backs in pencil as you print, following the tile numbers.
- Trim two edges. On every sheet except those in the first column, cut the left margin off exactly at the picture's edge. On every sheet except those in the first row, cut the top margin off the same way.
- Lay and match. Place each trimmed sheet over its left and upper neighbors so the trimmed edge sits on their white margin and the picture lines meet. Hold it with removable tape until a whole row lines up.
- Tape from the back. Turn the poster over and tape every seam along its full length, then trim the outer white margins.
If you would rather glue with overlap, make tiles with real overlap in an image editor and use the overlap column of the first table. It needs more sheets, but small misalignments disappear under the glued strip.
Tips that save paper
- Print one test tile and measure it with a ruler before printing the rest.
- Check the orientation in the table. An 18 × 24 inch poster takes 9 Letter sheets in portrait but only 6 in landscape, as a 2 × 3 grid.
- Use heavier paper if the poster will hang on a wall; the guide paper weight, gsm vs lb converts the weights.
- For a print shop, skip the tiles and send one file at full size; how to prepare a file for print covers bleed and color.
Frequently asked questions
How many sheets of paper do I need for a poster?
Divide each side of the poster by the printable width or height of a sheet and round up, then multiply the two counts. With Letter paper and a quarter-inch margin, the printable area is 8 by 10.5 inches, so a 24 by 36 inch poster takes 3 columns and 4 rows, 12 sheets, in portrait.
Should the tiles overlap?
Overlap makes alignment forgiving, because you can glue one sheet over the next and match the picture. It costs extra sheets. The alternative is to print tiles without overlap, trim the white margin off one side of each sheet, and lay that trimmed edge over the neighbor's white margin so the picture edges meet.
What resolution does a poster image need?
Multiply each side in inches by the pixels per inch you want. At 300 ppi, the figure the US Government Publishing Office design service asks for in photos, a 24 by 36 inch poster needs 7,200 by 10,800 pixels. At 150 ppi it needs half of each side. A poster seen from a few steps away tolerates less than a print held in the hand.
Why do my tiles not line up?
Usually the printer scaled them. Print every tile at 100 percent or actual size, never fit to page, and use the same setting for every sheet. Also check that all tiles come from one grid with equal tile sizes.
Can I enlarge a small image for a poster?
You can resize it to more pixels, but that does not add detail; it spreads the same detail over a larger area. If the image has too few pixels for the size, choose a smaller poster or accept a softer print.
Sources
- Wikipedia, Paper size: ISO 216 A series dimensions (A0 841 × 1189 mm with an area of 1 square metre, A1 594 × 841, A2 420 × 594, A4 210 × 297), the square root of 2 aspect ratio, US Letter 8.5 × 11 in, Arch D 24 × 36 in
- U.S. Government Publishing Office, Creative Services: Get started (photos a minimum of 4 × 6 inches at 300 dpi; images from the web have insufficient resolution)