The standard size of a sheet of A4 paper is 210 millimeters by 297 millimeters, or 8.3 inches by 11.7 inches, according to ISO 216 standard. A4 size paper is one-half of A3 size paper and one-quarter the size of A2 paper.
A4 paper size has an allowance of plus or minus 1.5 millimeters or 0.06 inches on each side, and standard paper sizes are rounded to the nearest millimeter. Letter size paper is 17.6 millimeters shorter than A4 paper, and legal size is 58.6 millimeters longer. A4 paper is the standard business letter size in countries that formerly used British Imperial sizes.