Choose the physical size
A4 and US Letter are different rectangles. Choose the paper loaded in your printer; shrinking an A4 sheet to Letter changes every grid interval. The tool leaves a generous 15 mm content margin for ordinary printers.
Measure a useful span
Print one sheet at 100% and measure ten squares, rather than a single tiny square. A 5 mm grid should measure 50 mm across ten intervals. If it differs, check driver scaling before modifying the file.
SVG has physical dimensions, but an editor can reinterpret its import units. PDF is the safer final printing format when your editor or browser applies an unexpected default.
Create and verify a specific sheet
Select Square graph paper, A4 and 5 mm spacing. Download the PDF and choose A4 paper in the print dialog. Turn off any option that says shrink, fit, scale to printable area or enlarge small pages. Print one test page before making a stack. Measure from the first line to the eleventh line to check ten intervals without counting the starting line as a square.
If that span measures 48 mm instead of 50 mm, the output is effectively 96 percent of the intended size. Look for scaling in both the document viewer and the printer driver; either can introduce it. Do not compensate by changing the grid to 5.208 mm unless you intentionally need a printer-specific workaround and have documented it.
Choose the right file for the next step
The PDF has a physical page box and is the preferred print handoff. SVG is useful when adding labels or adapting a grid in a vector editor, but check its imported units and page size. A screenshot or browser image preview has no reliable physical printing scale. For measurement-sensitive work, verify the paper output with a ruler after every change of printer or print settings.