Isometric dot paper, A4
The isometric lattice as dots rather than lines, on A4, the standard drawing size everywhere outside North America, and the one most technical drawing courses assume.
Opens with these settings already loaded. Change anything you like, then download as PDF, PNG or SVG.
Dots leave the drawing alone
A full isometric line grid is useful for construction but competes with the drawing once you start inking. Dots mark the same lattice points and then disappear behind the work. You get the geometry without the noise. This matters most when the finished sketch is meant to be read by someone else, which is the normal case for design and engineering work.
The spacing is measured along the axes, not vertically
On an isometric lattice the 5 mm figure is the distance between adjacent dots along the three drawing axes, not the vertical gap between rows. Rows sit closer together than that, by a factor of about 0.866, the sine of 60°. If you are counting dots to keep a solid square, count along the axes and ignore the vertical spacing entirely; it will not give you the answer you expect.
A4 and technical drawing convention
Outside North America, technical drawing is taught and examined on A4 and A3, and drawing boards, portfolios and sleeves are sized accordingly. If you are producing coursework, a sketch destined for an A4 report, or anything that will be filed alongside printed drawings, the A4 sheet saves you a trimming step and keeps margins consistent with everything else in the folder.
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.