The size of a standard U.S. postage stamp varies slightly, depending on whether the stamp is printed as part of a booklet or a roll. The Four Flags Forever stamp, printed as a booklet of 20 and issued in 2012, measures 0.87 inches wide by 0.98 inches high.
The stamp dimensions include the border around the edge of the stamp. Stamps issued on a roll are sometimes more narrow than those that are part of a booklet. The U.S. Postal Service uses multiple printers to produce stamps, and each printer produces a slightly different size. The difference in size is minute, usually less than a millimeter.