1RM Calculator
Estimate your one-rep max from any set of 1–12 reps, and get the working loads that follow from it.
How accurate is it
Within about 5% up to 5 reps. Past 10 reps every formula drifts, because rep endurance varies far more between people than maximal strength does. Test with a set of 3–5 if the number matters.
Which formula
Epley and Brzycki disagree by roughly 2–3% in the useful range. The default here averages four equations, which is more robust than trusting any single one.
The percentage table
The load table uses the Brzycki inverse, which is exact at one rep and matches the conventional %1RM charts. Your estimated 1RM above is the average of four equations, so the table and the estimate will disagree slightly unless you pick Brzycki explicitly, and that gap is the honest measure of how much these formulas are guessing.
- Epley, B. (1985). Poundage chart. Boyd Epley Workout, Lincoln NE.Self-published and not indexed; the equation is reproduced and tested in LeSuer et al. (1997).
- Brzycki, M. (1993). Strength testing: predicting a one-rep max from reps-to-fatigue. J Phys Educ Recreat Dance 64(1).Accurate to about 10 reps; drifts high beyond that.
- LeSuer, D.A. et al. (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res 11(4).Compared equations across bench, squat and deadlift.