In the print dialog choose A4 and leave the scale at 100%, or the squares come out a different size.
One board, 20 × 20 crossings
Take turns placing dots on the crossings. When your dots surround your opponent's with a closed line, draw round them — that ground is yours and is out of play. Whoever surrounds more when the paper is full wins.
A single lattice occupies almost the whole page — 20x20, which is four hundred intersections, drawn at 9.2 mm apart so a pencil behaves exactly as it does on the smaller sheet. Only the spacing is shared; everything else is scale. Above the lattice the rules are printed in full, and beneath it there is space to write down who played and how the territory finally divided.
Choose the large board when both players already know what they are doing and want a proper contest. Territory does not resolve quickly here: separate skirmishes open in different corners, survive independently for a long while, and only join up towards the end, which is where the interesting decisions live. Expect three quarters of an hour or more for one game, and expect to spend part of it deciding which fight to abandon. It is the tournament shape of the game rather than the coffee-break shape. Keep an eraser nearby: a misjudged boundary is worth undoing before it hardens into a position.
Choose A4 and leave the scale at 100%. Any other value shrinks the drawing, and a square that should measure 9.2 mm comes out smaller — which matters, because these boards are sized for a real pencil rather than for a screen. Ordinary 80 gsm copier paper is enough; anything heavier resists a fold. If your dialog offers “fit to page”, switch it off, then check the printed square against a ruler before you start playing.