Crochet chart paper, A4
Crochet chart paper on A4, with cells taller than they are wide because crochet stitches are.
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Check which terminology your pattern uses
This matters more than the paper. US and UK crochet names are offset by one: a US single crochet is a UK double crochet, a US double is a UK treble, and so on up. A pattern that calls for double crochet means two different stitches depending on which side of the Atlantic wrote it, and the resulting fabric differs in height by a noticeable amount. Since stitch height is exactly what sets your cell proportion, charting from a pattern in the other convention will give you a chart that is wrong in a way the chart itself cannot show you. Look for a note near the top, or infer it from whether the pattern says "gauge" or "tension".
Stitch height varies far more than in knitting
A knit stitch is reliably a little wider than tall, and the ratio moves within a fairly narrow band. Crochet has no such stability. A single crochet is close to square, a half double is taller, a double crochet is much taller again, and a treble taller still. Charting a double crochet design on paper ruled for single crochet distorts it badly. Swatch the stitch you will actually work, count stitches and rows over the same distance, and enter both into the generator so the cells match.
A4 and European pattern sources
Most crochet publishing outside North America is on A4, and a great deal of the pattern archive that circulates online is European or Japanese in origin. If you are printing charts to file alongside those, A4 saves trimming and keeps the punch holes lining up. Japanese crochet patterns are worth knowing about separately: they are written almost entirely in symbol charts rather than words, which means you can work them without reading Japanese, and they assume a chart grid rather than a written row list.
Printing it accurately
This only measures correctly if your printer doesn't rescale the page. In the print dialog set Scale: 100%, not "Fit to page" or "Shrink oversized pages". If you're not sure it worked, print the calibration page, measure the ruler on it with a real ruler, and it will tell you exactly what your printer is doing to the page.