One Rep Max Calculator

Within a few percent when fed a true hard set of 2–6 reps — accurate enough to program from. Accuracy fades as reps climb because endurance starts mattering more than strength; past 15 reps the estimate is closer to folklore, which is why the calculator caps there.

Different curve fits to the same phenomenon: Epley (weight × (1 + reps/30)) runs slightly higher at high reps, Brzycki (weight × 36/(37 − reps)) slightly lower. They agree almost exactly at 2–10 reps, so the averaged figure is a solid programming number.

For training, no — percentage-based programs work perfectly off estimated maxes, and a rep-max test (say, a hard set of 3) carries far less injury risk than a grinding true single. True maxes are for meets and milestones, ideally with spotters.

Programs prescribe sets like '5×5 at 75%.' Find 75% in the table, load the listed weight (already rounded to 5s), and note the typical-reps column as a sanity check — if 75% feels like a 3-rep max, your estimate is stale or today isn't the day.