Look up ISO A/B/C, US Letter/Legal/Ledger and Chinese paper sizes, or match your own dimensions.
Match nearest standard
Pick a series (A/B/C, US, Chinese) and number to see exact dimensions in mm and inches, plus the sheet area. The Match tool takes a width × height in mm and finds the closest standard size (orientation is normalized — your wider side is matched against either side of the standard). The A series overview lists A0 → A10, each one half the area of the previous.