Five feet six inches !
Anything you like as long as one of them is greater than or equal to sqrt(409). Let L be any length greater than sqrt(409) feet and let B = 409/L feet Then L*B = L*(409/L) = 409 sq feet.
12 feet, 6 inches
681 inches = 56.75 feet (56 feet 9 inches).
5 feet 4 inches
125 inches is equal to 10.4167 Feet.
5 feet 3 inches
12 feet 8 inches
There are 6 feet in 72 inches.
10,284 inches in 857 feet.
180 inches in fifteen feet
1,055 inches = 87.9166667 feet