If each number is multiplied by 1000 (moving decimal point 3 places to the right), it becomes much easier to compare their sizes:
340, 400, 34, 304, 314→(smallest to largest) 34, 304, 314, 340, 400→0.034, 0.304, 0.314, 0.340, 0.400 so 0.034 is smallest.