One Rep Max Calculator

The one-repetition maximum (1RM) is the maximum weight you can lift for a single repetition of an exercise with good form. It is the gold standard for measuring strength and is used to calculate training percentages

The calculator uses the standard published formula for one rep max. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

This calculator works with inches, percentages. You can enter values in the units shown — the calculator handles all conversions internally.

The core formula is: Epley (1985): 1RM = weight × (1 + reps/30). Each step in the calculation is shown so you can verify the result manually.