Graph paper that is the size it says it is PAPER

Graph paper printed from a PDF is almost never the size it claims

The browser fits the page to the sheet. The driver applies “shrink to printable area” so the margins are not clipped. A 5 mm grid comes out at 4.8 mm and nothing anywhere reports it.

For a shopping list that does not matter at all. For a scale drawing, a knitting chart, a plot you are going to measure off, a pattern, or a site sketch somebody else will build from, it is the difference between a drawing and a decoration. And the error is invisible from the inside, because every square is wrong by exactly the same amount: the grid looks perfectly regular, so there is nothing to notice.

Two things a PDF cannot do for you

The grid here is generated as SVG in real millimetres. The drawing is 210 mm wide because its width attribute says 210mm and its user units are millimetres, and the @page rule sets the sheet to match with no margin. There is nothing left for the browser to fit, so the usual scaling step has nothing to act on.

And every sheet can carry a 100 mm ruler printed in its margin. That is the part that actually settles it. Print the sheet, put a ruler against the printed ruler, and you know: not from a setting, from the paper in your hand. If it reads 97 mm, the print was scaled to 97%, and you can go and turn that off rather than wondering.

Keep the ruler on for anything you will measure from. It costs a strip of margin and it means the sheet carries its own proof, which is worth having a month later when you cannot remember what settings you used, and worth much more when somebody else is working from your drawing.

Setting the print dialogue

Scale must be 100%, or “Actual size”. Not “Fit”, not “Shrink oversized pages”. Margins to none or minimum. Set the paper size to the one the sheet was drawn for, because A4 art on US Letter is a scaling instruction however it is phrased.

Then check the ruler. Every time you change printer, and once for each printer you use regularly; most people only ever need to do it once, and then they know.

Ten kinds of paper are here: square grids at the common pitches, engineering and quadrille, dot grid, isometric and triangular for projections and for knitting, hexagonal, lined at several rulings, music manuscript, and plain millimetre paper. All drawn the same way, all with the same ruler available.

Related: ENVELOPE and LABELS deal with the same problem from the other end (print geometry that has to match a physical object), and BOOKLET puts pages in the order a folded booklet reads. Nothing here is uploaded; the sheets are drawn in the tab.