Print a poster across sheets of A4

How do you print a poster on A4 sheets?

Drop in the picture, choose how many sheets across and down, and press Save PDF. You get a PDF with one A4 page per sheet, each holding its piece of the picture. Print the lot, trim the white edges, and tape them together from the back.

The whole thing happens on your computer, so a photograph of your own class can be blown up for a display without it passing through anybody’s server on the way.

How many sheets do I need?

Four sheets in a 2 × 2 gives you about A2, nine sheets about A0, and sixteen is bigger than most classroom boards. The tool prints the finished size in centimetres as you change the grid, so you can hold it against the space in your head.

Sheets	Roughly	What it suits
2 × 2 (four)	42 × 59 cm, about A2	A working wall heading, or one panel of a bigger display.
3 × 3 (nine)	63 × 89 cm, about A1–A0	The usual answer. Fills most of a standard classroom board.
4 × 4 (sixteen)	84 × 119 cm, about A0	A corridor or hall display, and about as much taping as anyone wants to do.

Show all of it, or fill every sheet?

Your picture and your grid are almost never the same shape, so something has to give. Show all of it keeps the whole picture and leaves some edge sheets blank, which you throw away. Fill every sheet enlarges the picture until it covers the grid, cropping the edges to make it fit.

For a photograph, filling is almost always right — losing a strip of sky costs nothing. For anything with words or a border, show all of it, or you will discover the crop went through the title.

How do you join the sheets up?

Trim the white margin off the sheets that meet, overlap the joins by two or three millimetres, and tape from the back. The trimming is the part people skip, and it is the reason home-made posters look home-made: every printer leaves an unprintable border, and untrimmed sheets leave a white grid across the picture.

Work outwards from the middle sheet rather than starting at a corner, and the small errors spread out instead of piling up at one end.

Why do the joins not line up?

Nearly always because the printer was left on “fit to page” or “shrink to fit”, which quietly shrinks every sheet by a few per cent. Each one is then slightly too small, and the error accumulates across the poster. Print at 100%, actual size, no scaling — it is the single setting that decides whether this works.

Will it look pixelated?

It depends entirely on what you started with, because blowing something up cannot invent detail that was never there. A photograph off a modern phone will hold up across nine sheets easily. A small picture pulled off a website will not, and no tool can fix that — it will look soft however it is printed.

The quick test: if the picture looks sharp on your screen at full size, it will be fine. If it already looks soft, it will look four times softer on a wall.

What do teachers make with it?

Working-wall headings, a giant number line, a map for a topic, an enormous photograph of the class for the corridor, a book cover blown up for a reading display, and a large diagram for the front of the room. All of them are one picture and a grid, which is why this is one tool rather than six.