How to print a big poster on A4 paper
You do not need a large-format printer to make a big poster. Split the picture into A4 pages, print them on a normal home printer, and join them. This guide covers every step, from choosing a picture to taping the last sheet.
1. Choose a picture that is big enough
Sharpness matters more as the poster grows. A rule of thumb is at least 100 pixels per inch of the finished poster. For a poster 60 cm (24 in) wide, that means a picture about 2400 pixels across. Phone photos are usually 3000 to 4000 pixels wide, which is plenty for a poster up to about 80 cm wide. The poster maker warns you when the picture is too small.
2. Pick the number of sheets
Choose how many sheets wide the poster should be. Leave sheets down on Automatic and the tool matches your picture’s shape, cropping a little if needed. Use “Show whole picture” if you do not want anything cropped; you will get white bars instead.
3. Keep the overlap at 8 mm
Home printers leave an unprintable border of roughly 3 to 6 mm around each page. The overlap pushes the picture past that border so nothing goes missing. Each sheet carries an extra strip on the left and top that you trim off. Raise the overlap to 12 mm or more if you want a wider area for glue or tape.
4. Print at 100% scale
This is the step most people get wrong. In the print dialog, choose Actual size or 100% and turn off “Fit to page” or “Shrink oversized pages”. Otherwise the printer shrinks each page and the picture will not line up. Pick the highest paper quality your printer offers, and print a single test page first.
5. Trim the marked strips
Each sheet has small black tick marks on its edges. Cut along the line between the marks to remove the strip on the left edge and the top edge. The first sheet in each row loses nothing on the left, and the first row loses nothing at the top. A paper trimmer or a metal ruler and a craft knife gives cleaner edges than scissors.
6. Assemble from the top left
Lay out the sheets in number order, left to right, top to bottom. Join each row first by taping the back of neighbouring sheets, then join the rows. Double-sided tape or a glue stick along the overlap gives the neatest result. Mount the finished poster on foam board or hang it with removable adhesive strips.
Troubleshooting
- Sheets do not line up. The printer scaled the pages. Reprint at 100% with “Fit to page” turned off.
- White gaps between sheets. The overlap was too small for your printer’s margin. Increase it to 10 or 12 mm and print again.
- Picture looks blurry. The picture has too few pixels for that poster size. Use a larger picture or fewer sheets.
- The PDF will not finish on my phone. Choose Draft print quality, or use fewer sheets.
- I use US Letter paper. Choose Letter in the paper setting.