A4 is metric
A4 measures 210 x 297mm and is the common paper size in many countries. It pairs naturally with 5mm and 1cm graph paper.
A4 vs Letter Graph Paper
A4 and Letter are similar but not identical. Choosing the correct paper size matters when the grid needs to print accurately.
Letter is common in North America
Letter measures 8.5 x 11 inches and is the common paper size for US and Canadian classrooms, offices, and home printers.
Do not rely on printer scaling
Printing an A4 template on Letter paper, or the reverse, can shift margins and scale the grid. Pick the matching template when possible.