One picture across several sheets of paper POSTER

An ordinary printer makes a poster perfectly well

Wanting something bigger than A4 is an ordinary thing to want: a floor plan, a chart for a wall, a sign, a seating diagram, a pattern at full size, and the answer everybody is given is a print shop. The print shop is a day and a cost for something that is usually needed this afternoon.

The actual answer is that the printer on the desk does it, if the image is cut into pages first. The arithmetic is easy. The fiddling is not, and the fiddling is where people give up: working out the grid, getting the overlap consistent, exporting twelve crops in the right order, and then identifying which sheet is which when they come out of the tray face down.

So that is what is done here. You give it a picture and a finished size; it works out the grid and the overlap, and prints the pieces with trim marks and a label on each edge, so a pile of twelve sheets can be assembled without guessing.

The overlap is not optional

A poster tiled edge to edge cannot be assembled. Every desktop printer has an unprintable margin (a few millimetres it physically cannot put ink on) so tiles cut exactly to size come out with a white band around each one, and butting them together leaves a visible gap at every join. Trimming to the image edge is impossible because the image edge is inside the white band.

A real overlap solves both. Each sheet carries a strip of its neighbour's content, you trim one sheet along its trim mark, and lay it over the next so the picture runs continuously. The join disappears because there is material to lose.

Make it generous on anything with fine detail or continuous tone. Ten millimetres is comfortable; five is tight if your hands are not steady, and the overlap costs only paper.

Assembling it

Print scale must be 100%, or “Actual size”. Every tiling scheme assumes it, and “Fit to page” silently shrinks each tile by a percent or two, which does not look wrong on one sheet and means nothing lines up across twelve.

Lay all the sheets out unfolded before you cut anything, in the grid, using the edge labels. It takes a minute and it catches a missing sheet or a rotated one while that is still easy.

Then work in one direction: trim the right edge of every sheet in a column, join the columns into strips, trim the bottom of each strip, and join the strips. Trimming everything first and then assembling is how you discover you trimmed the wrong edge on sheet seven. Overlap consistently (always the left sheet over the right, always the top over the bottom) because alternating shows as a ridge under a light.

A glue stick along the overlap, not tape, if the poster will be photographed or scanned: tape catches the light on every join. Nothing is uploaded; the image is cut in the tab. Alongside, PAPER prints graph and ruled paper at a size you can prove, BOOKLET puts pages in the order a folded booklet reads, and LABELS prints a sheet measured in millimetres.