How do you figure out the percentage of 1 RM for resistance in weight training?

The amount of weight to be used should be based on a percentage of the maximum amount of weight that can be lifted one time, generally referred to as one repetition maximum (1RM). The maximum number of repetitions performed before fatigue prohibits the completion of an additional repetition is a function of the weight used, referred to as repetition maximum (RM), and reflects the intensity of the exercise. A weight load that produces fatigue on the third repetition is termed a three repetition maximum (3RM) and corresponds to approximately 95% of the weight that could be lifted for 1RM.