The first check: the 100 mm line must be 100 mm long, and the 2 inch line must be 2 inches long. Measure between the end ticks with a ruler. A screen preview is not a physical ruler.
Use page 1 as a small test
FirstPrint adds a calibration page to every poster PDF. It has a 100 mm line, a 2 inch line and a 1 inch square. Print only that page on the selected A4 or Letter paper, with the same orientation that the PDF uses.
- In your PDF viewer, select Actual size or 100%. Turn off Fit, Shrink, Scale to fit and borderless enlargement. Names vary between viewers and printer drivers.
- Select single-sided printing and the matching paper size in both the viewer and printer settings.
- Measure the printed lines and the square. If they are wrong, change the print settings and print this page again before committing to the poster.
Do not resize the original poster to compensate for a printer setting. That can hide the problem while changing the promised finished dimensions. The calibration page and all poster sheets need the same scale.
What the measurements tell you
| What you find | What to check next |
|---|---|
| 100 mm line prints at 98 mm | The output is 2% smaller along that direction. Look for automatic Fit or Shrink settings and a paper-size mismatch. |
| Line is correct, image edge is missing | Check the printer's minimum margins. Correct scale does not guarantee that it can print close enough to each paper edge. |
| Horizontal and vertical square sides differ | Repeat the measurement. If the difference persists, check the driver and printer. Software page geometry cannot guarantee paper-feed accuracy. |
| Every line is right, but joins mismatch | Check the assembly order and overlap. Confirm that all sheets came from the same PDF with the same print settings. |
| Scale is right but the image is blurry | Check effective DPI, original image quality and print quality. Changing the print scale does not create image detail. |
Leave space for the image and the guides
The selected margin is the distance from the paper edge to the image area. Trim marks and sheet labels sit in that margin. When using printed guides, choose a margin at least 4 mm larger than your printer's minimum; the default 10 mm margin may still need to be increased for your printer.
For example, if your printer needs 6 mm of unprintable space, a 10 mm margin leaves room for the guides. If the printer needs 8 mm, use at least 12 mm. Increasing the margin reduces the image area on each sheet and may increase the sheet count. Recheck the live preview after changing it.
Guide lines are only cut references; they are not a command to trim away the shared picture strip. Keep that strip when assembling an overlapped poster. The orange overlap tint in the single-sheet preview is a visual aid and is not printed into your photograph.
Check a join before trimming every page
Lay out A1 and B1 using PDF page 2's assembly map. Trim their white edges at the marks and align the repeated picture. With the default 5 mm overlap, B1 covers the last 5 mm of A1's image. Work across the row, then down through the rows. Tape on the back when the image lines up.
If you selected 0 mm overlap, the PDF gives different instructions: butt the image edges together. There is no repeated strip to align. Use a straight cut and avoid adding or removing space between sheets.
A final row or column may be narrow when you set an exact poster size. Keep it if you need those exact dimensions. For a worked example of the 30 × 16 mm corner on a 400 × 560 mm poster, see printing an image on multiple pages.
Calibration questions
Can I measure the line on my phone screen?
No. Screen zoom, pixel density and browser layout change its displayed size. The reference is the PDF's physical output, so measure a printed page. The tool does not claim to calibrate your printer automatically.
Should I use borderless mode to remove the white edges?
Borderless modes can enlarge the image or trim edges. This workflow is designed around ordinary margins and exact scale. Use the selected margins, Actual size and the trim marks; do not assume borderless mode preserves the poster dimensions.
How do I retry without losing my work?
Keep the downloaded PDF to reprint selected pages. Save a FirstPrint project to preserve the source image and settings for later edits. If PDF generation is interrupted, Cancel returns you to the same image and layout so you can retry. Refreshing without saving clears the working image.
Make a PDF with its own test page.
The calibration page and assembly map are included automatically, before the poster sheets.
Make your poster PDF →What has been verified: the exported PDF's A4 and Letter page sizes, the 100 mm / 2 inch calibration vectors, image placement and overlap pixels were checked with an independent PDF parser. These are digital checks, not a claim that we tested a physical printer.
Source and scope: the Rasterbator printing FAQ also describes Actual size and printer-margin issues. The worked measurements and retry instructions here describe FirstPrint's own output. There is no guarantee of a particular printer's mechanical accuracy, colour or paper feed.