1RM (One Rep Max) Calculator

Understanding 1RM (One-Repetition Maximum)

Your one-repetition maximum (1RM) is the heaviest load you can lift one time with proper form. Testing a true 1RM is risky for untrained lifters, so coaches usually estimate it from submaximal sets with regression equations. The two you'll see quoted most often are Epley, 1RM = w × (1 + r/30), and Brzycki, 1RM = w × 36/(37 - r). Here w is the load you lifted and r is the number of clean reps you got to concentric failure.

Both equations hold up well for sets of 2 to 10 reps. Once you push past about 10, neuromuscular fatigue and the aerobic contribution start to skew the prediction, and the estimate drifts. Averaging a couple of formulas smooths out the bias in any single one and leaves you with a sturdier working number.

Applications

The ACSM and NSCA write strength loads as a percentage of 1RM. Roughly 85% covers 5RM strength and hypertrophy work, 75-80% lands you in 8RM hypertrophy territory, and 90% or more is where max-strength singles and doubles live. Having a 1RM estimate is what lets you add weight safely, lay out training cycles, and stack athletes against each other on relative strength, all without a maximal attempt every single week.

FAQ

Is the estimate accurate above 10 reps? Not really. Validity falls off fast once the endurance and lactic systems take the wheel. Stick to 3-8 reps if you want the tightest estimate.

Epley or Brzycki — which is better? At high reps Brzycki leans a touch low while Epley runs high, so in practice averaging the two is a sensible compromise.

Do I need to test 1RM directly? Most lifters never do. A heavy set of 3-5 reps gives you an estimate that's safer to chase and tells you almost everything you need for programming.