A-series vs US paper sizes
A-series sizes (A2, A3, A4, A5, A6) follow the ISO 216 standard: each size is exactly half of the one before it, so an A4 sheet folded in half becomes A5. US sizes – Letter, Legal and 11×17 (Tabloid) – are measured in inches and are slightly wider and shorter than their nearest A-size.
Always print a PDF on the paper size it was made for and keep the scale at 100% so the grid spacing stays accurate.