The work output of a machine divided by the work input is the efficiency of the machine. Efficiency is typically stated as a percentage and is calculated by dividing work output by input and then multiplying by 100.
The reason to use a simple machine ? for instance, a lever ? is that this type of machine can multiply the amount of force input to result in a larger force output than input. This is called the mechanical advantage. In contrast to force, work output cannot be any larger than the work input. Simple machines take work input that is equal to a small force over a large distance and output a large force over a small distance.