For a 30°-60°-90° triangle, the sides will have a ratio of 1:sqrt(3):2. Therefore if the shortest side (across the 30° angle) has a length ratio of 1, then the longer leg has a length ratio of sqrt(3). Therefore we have the proportion:
3 inches/1 = x/sqrt(3)
x = 3sqrt(3) inches
Note that the side of length ratio 2 is the hypotenuse, not the longer leg.