Why Calculate Your 1RM?
Knowing your 1-Rep Max is critical for almost all structured strength and powerlifting programs (like 5/3/1, Sheiko, or Smolov). These programs do not tell you to lift a specific weight; rather, they tell you to lift a specific percentage of your 1RM. For example, a workout might prescribe 5 sets of 5 reps at 75% of your 1RM. Without knowing your max, you cannot follow the program accurately.
The Danger of Testing Your True Max
Testing a true 1-Rep Max is physically exhausting, taxes your central nervous system for days, and carries a high risk of injury—especially if you do not have experienced spotters. By using a calculator, you can lift a moderately heavy weight for 3-5 reps (which is much safer) and mathematically determine what your absolute max would be.
The Math Behind the Calculator
There are many formulas used to calculate a 1RM. Our calculator averages the two most respected and empirically tested formulas in sports science:
The Epley Formula
1RM = Weight × (1 + Reps/30)Created in 1985, this is the most widely used formula in the world.
The Brzycki Formula
1RM = Weight × (36 / (37 - Reps))Created in 1993, this formula is highly accurate for rep ranges under 10.