Answer is: edge of the length of the box measured is 1280,57 kilometers.
V(raindrop) = 3,48 cm³.
V(cubic box) = 3,48 cm³ · 6,023·10²³.
V(cubic box) = 2,1·10²⁴ cm³.
V(cubic box) = 2,1·10²⁴ cm³ ÷ 10¹⁵.
V(cubic box) = 2,1·10⁹ km³.
r(cubic box) = ∛2,1·10⁹ km³.
r(cubic box) = 1280,57 km.
