One Rep Max Calculator
Estimate your one-rep max (1RM) for any lift from a weight and rep count.
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Enter your values and click Calculate
How It Works
Uses the Epley formula: 1RM = weight × (1 + reps ÷ 30). This is the most widely cited formula in strength training research and is accurate for most lifters performing sets in the 2–10 rep range. The formula assumes that each additional rep beyond one represents approximately a 3.33% reduction from true max effort. Once you have your estimated 1RM, the calculator breaks it into standard training percentage zones — 90%, 80%, 70%, and 60% — which correspond to the heavy single, strength, hypertrophy, and endurance rep ranges used in modern programming. Estimates become progressively less reliable above 10 reps.
Examples
100 kg for 5 reps
A typical working set for an intermediate lifter.
Result: Estimated 1RM ~117 kg.
225 lbs for 3 reps
A heavy triple on the bench press.
Result: Estimated 1RM ~247 lbs.
60 kg for 8 reps
An intermediate squat working set.
Result: Estimated 1RM ~76 kg.
Frequently Asked Questions
How accurate is the Epley formula?
It is a reliable estimate for most people performing sets in the 2–10 rep range. Accuracy decreases above 10 reps because fatigue, endurance, and technique become larger variables. Actual 1RM can also differ based on daily readiness, bar speed, and individual strength curves.
Should I ever attempt my 1RM in training?
Max attempts carry a higher injury risk and should only be attempted by experienced lifters with proper warm-up, a qualified spotter, and a safe setup. For most recreational athletes, using a calculated estimate from a heavy submaximal set is safer and practical enough for programming purposes.
What training percentage should I use for muscle growth?
Hypertrophy (muscle building) is most effectively stimulated in the 65–80% of 1RM range, corresponding roughly to 8–15 reps per set. Strength development is typically trained at 80–90% for 3–5 reps, while peaking or max strength work occurs above 90%.