Standard Orthogonal Arrays Maximum Number of Columns at These Levels Orthogonal Array Number of Rows Maximum Number of Factors 2 3 4 5 L 4 4 3 3 - - - L 8 8 7 7 - - - L 9 9 4 - 4 - - L 12 12 11 11 - - - L 16 16 15 15 - - - L’ 16 16 5 - - 5 - L 18 18 8 1 7 - - L 25 25 6 - - - 6 L 27 27 13 1 13 - - L 32 32 31 31 - - - L’ 32 32 10 1 - 9 - L 36 36 23 11 12 - - L’ 36 36 16 3 13 - - L 50 50 12 1 - - 11 L 54 54 26 1 25 - - L 64 64 63 63 - - - L’ 64 64 21 - - 21 - L 81 81 40 - 40 - -