This calculator estimates your one rep max from a hard working set. You enter the weight and reps you completed, and it uses well known strength formulas to estimate what you could lift for a single rep. For lower rep sets, it uses an average of the Epley and Brzycki formulas, which tend to track well when reps are closer to maximal effort. As reps increase, the calculator switches to the Mayhew formula, which is generally more stable for higher rep sets. Different formulas behave better at different rep ranges, so the calculator adjusts the method automatically based on how many reps you enter.

The calculation itself doesn’t change by lift. A set of 100 kg for 5 reps is treated the same mathematically whether it’s a bench, squat or deadlift. Different lifts fatigue in different ways. Bench press usually drops off faster as reps increase, which means higher rep sets can overestimate strength. Deadlift is often most accurate at lower reps because fatigue builds quickly and technique can change as reps climb. Squat tends to sit somewhere in between, with moderate accuracy across a wider range of reps compared to bench or deadlift.