A 30 60 90 triangle is a special triangle that has simple proportions for it's side lengths. The short leg to long leg ratio is 1:sqrt(3); the short leg to hypotenuse ratio is 1:2. If the length of the short leg (across from the 30 degree angel) is 6.25 cm long, then the length of the hypotenuse is twice that: 12.5 cm.