What is the equation to the MA (Mechanical Advantage) of a screw

A certain amount of energy can be saved by the use of simple machines like screw, wedge, levers etc., the measure of this energy is called as the mechanical advantage. Screw is one of the simple machines with helical ridges and head. The helical ridges are called as thread. Find the mechanical advantage of the screw with this online calculator.

If the diameter of the screw is 4m, and length is 7m, then

MA = 3.14 * 4 / 7

MA = 1.7952