B size

B size

[′bē ‚sīz]
(engineering)
One of a series of sizes to which trimmed paper and board are manufactured; for size BN, with N equal to any integer from 0 to 10, the length of the shorter side is 2-N /2meters, and the length of the longer side is 2(1-N)/2meters, with both lengths rounded off to the nearest millimeter.
Of a sheet of paper, the dimensions 11 inches by 17 inches (279 millimeters by 432 millimeters).