The actual mechanical advantage is determined by dividing the resistance force (Fout) by the effort force (Fin). Both the output and input forces are determined experimentally.
The AMA of a machine tends to differ from the theoretical, or ideal, mechanical advantage when friction is considered because some effort is lost in overcoming friction. This difference is significantly low in some machines like levers but high in others like pulley systems.
The efficiency of a machine is calculated by dividing the AMA by the ideal mechanical advantage. Since efficiency is represented as a percentage, the resulting answer is multiplied by 100.