Printable graph paper at the exact millimetre size you ask for

Almost always because the print dialog scaled it. Chrome, Edge and Safari all offer to fit the page to the printable area, and because printers cannot print to the very edge of the paper, “fit” means “shrink” — typically to somewhere between 94% and 97%. At 96%, 5 mm squares print at 4.8 mm, which is invisible on one square and obvious across twenty. Set Scale to 100% explicitly rather than leaving it on a fit option, and confirm the paper is A4 and not Letter, which is 6 mm narrower and 18 mm shorter and will trigger a fit-to-page shrink of its own. The second cause, much rarer, is a driver set to “scale to fit printable area” at the operating-system level, which overrides the browser; if ten squares still measure short after setting 100%, that is where to look.

Because a repeating pattern is a CSS background image, and Chrome’s print dialog has a “Background graphics” checkbox that is switched off by default and strips every background on the page. The sheet then prints completely blank — no error, no warning, just white paper. This is not a theory: it was found in this codebase on a different tool, by generating the PDF twice and reading the colour operators out of the file, and `print-color-adjust: exact` does not override the checkbox. Lines and dots drawn as SVG shapes are content rather than decoration, so they print whether that box is ticked or not. The cost is a larger file at very fine spacings, which is why the tool shows you the mark count.

For plotting graphs in mathematics and science, 5 mm is the common default and 1 cm is the version that suits younger hands and larger axes. For anything where a pupil writes a digit inside each square — place value, column arithmetic, times-table grids — 1 cm is about the smallest that stays writeable in pencil. For scale drawing and design technology, quarter inch at 6.35 mm exists because the drawing conventions and the rulers are imperial. For sketching and diagrams, dots at 5 to 8 mm give you structure without printed lines showing through the work. And 2 mm exists for the same reason millimetre paper always has: fine data plotting where you want to read a value between the gridlines. The honest answer is that these are conventions rather than rules, and the sheet costs nothing to reprint at a different size.

Isometric paper is for drawing three-dimensional objects on flat paper without perspective. The three line directions — vertical, 30° up to the right, 30° up to the left — correspond to the three axes of a cube seen corner-on, so a unit cube is drawn as three identical rhombuses and every edge of the same real length is the same length on paper. That is what makes it useful: you can measure a drawing made on it. Horizontal lines would not correspond to any axis of that projection, which is why they are absent, and it is the difference between isometric paper and triangle paper — the latter is the same grid rotated, and is used for tessellation and pattern work rather than for solids. The spacing control here sets the triangle side: the distance between neighbouring points along any one of the three directions.

Grey, unless the sheet will be copied. A grid exists to guide work that goes on top of it, and if the grid is as dark as the pencil, the pupil’s work stops standing out — which is also why commercially printed graph paper is usually pale blue or green rather than black. Light grey has the side benefit of using perhaps a third of the toner of a black grid, which matters at thirty copies a week. The exception is photocopying: copiers and document scanners raise contrast aggressively and pale grey is exactly what they drop first, so if the master will be copied rather than reprinted, use black or at least the mid grey. The same logic applies to line weight — a 0.1 mm hairline is clean off a laser printer and often gone after one generation of copying.

Two reasons, one physical and one deliberate. The physical one is that consumer printers hold the paper with rollers and cannot lay ink in a band of roughly 3 to 5 mm around the edge, more at the trailing edge on some inkjets; a grid drawn into that band is simply not printed, and the sheet looks miscut. The deliberate one is that this tool only draws whole squares. It divides the drawing area by your spacing, discards the remainder and centres what is left, so both edges get the same partial gap and every square on the page is a full square. Half squares at the right-hand edge look like a printing fault even when the full squares are perfectly sized, and they mean a pupil counting from the right gets a different answer from one counting from the left.

Yes — that is the “heavier line every” control, and it accepts 2, 4, 5 or 10 squares. It draws the emphasised line at double the weight you chose rather than in a second colour, which is on purpose: a second colour would mean a second ink setting and a second way for the sheet to come out wrong, while double weight is what surveyor’s and engineering pads have always done and it survives photocopying. It is available on square grids only. On a dot grid there is no line to thicken, and on isometric paper the three families would need three separate emphasis rules to stay coherent, which is more machinery than the feature is worth.

No. The whole page is static files and the grid is drawn by your own browser, so there is no server for anything to be sent to; there is also no saved setting, no cookie of ours and no draft — close the tab and the sheet is gone, which is fine for something that takes eight seconds to set up again. Printing works by building a small self-contained document and handing it to your browser’s own print dialog, and the “Download as SVG” button writes that same drawing straight to your disk. One honest note: this site carries Google ads, which are a third-party request like on any ad-supported page, and they are not part of the printed sheet.

Because the SVG carries its dimensions in millimetres, so it opens at the correct physical size in Inkscape, Illustrator, Word or a slide deck, and you can drop a grid into a worksheet you are already writing instead of printing it separately. It is also a way out of a print dialog that will not behave: an SVG placed into a document is scaled by that document, not by the browser, so if your printer setup insists on shrinking web pages you can still get an exact grid onto paper. And because it is vector, enlarging it to A3 costs nothing in quality — the lines stay the weight you chose relative to the squares.