Make the seams meet.

Try two neighboring sheets before printing the whole poster.

Two-sheet seam check

1. Check the first PDF page with a ruler. Both axes must read 100 mm.
2. Print two horizontally adjacent poster sheets at 100%, such as R1 C1 and R1 C2.
3. Use the corner marks to trim the white left margin from the right sheet. Keep its repeated image strip.
4. Place that strip over the matching image on the left sheet. The image repeats by the selected overlap (5 mm by default); align the artwork, then tape from behind.
5. Repeat vertically: trim the top white margin from the lower sheet and align its repeated top strip. Trim remaining outer margins and unused white space after assembly.

The join repeats part of the picture

Overlap is intentional. Stack matching artwork instead of placing the printable rectangles edge to edge. With 0 mm overlap, butt the trimmed image edges together; this is less forgiving.

The marks or edges are missing

Your printer may require more than 5 mm of unprintable margin. Increase Print margin in the tool, export again, and repeat the check sheet. Do not enable Fit to recover the marks.

One direction aligns but the other does not

Confirm that paper size and orientation match the PDF. Disable borderless expansion and scaling. Reprint the calibration page and measure both axes. The PDF cannot control the printer driver.

The export is too large or the browser stops

Resize the source locally, reduce poster dimensions or overlap, and close other heavy tabs. Start again with a smaller JPG or PNG. The limits are 20 MiB, 24 megapixels, 12,000 px per side and 100 poster sheets plus 1 check sheet. Some devices may need smaller images.