One Rep Max Calculator
Estimate your one rep max from any set. See Epley, Brzycki, and Lombardi results plus a percentage chart for programming. Free, no signup required.
What is a one rep max?
Your one rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It is the standard measure of maximal strength and the basis for programming training intensity via percentages — most structured programs prescribe loads as a percentage of your 1RM.
Testing an actual 1RM carries injury risk, requires extensive warm-up and full recovery, and is impractical to do frequently. Estimating your 1RM from submaximal sets is safer, more practical, and nearly as accurate for sets of 2–10 reps. This calculator uses three validated formulas and averages them for the most reliable result.
How to estimate your one rep max
The most practical way to estimate your 1RM is from a submaximal set — lift a weight for multiple reps, then apply a validated formula. This calculator uses three established formulas and averages them for the most reliable result.
Epley formula
The most widely used 1RM estimation formula. 1RM = weight × (1 + reps / 30). Epley tends to estimate slightly higher at low rep ranges (1–5 reps). The formula is linear, which means it can overestimate at 15+ reps where fatigue dynamics change. This is the formula Evid uses internally for automatic e1RM tracking.
Brzycki formula
Slightly more conservative than Epley. 1RM = weight × 36 / (37 − reps). Produces lower estimates at 1–5 reps and converges with Epley at 6–10 reps. Mathematically unstable above 36 reps, but this is not practically relevant for strength training.
Lombardi formula
An exponential approach. 1RM = weight × reps0.1. The most conservative of the three across all rep ranges. Less commonly used in practice but included here for comparison and to improve the accuracy of the averaged result.
Which formula should you use?
The average of all three is the most reliable estimate. For training in the 3–6 rep range, both Epley and Brzycki are individually accurate. All three formulas become less reliable above 10 reps — treat high-rep estimates as rough approximations rather than precise predictions.
How to use your estimated 1RM
Percentage-based training
The traditional approach prescribes loads as percentages of your 1RM. Strength work lives at 85–95% (1–5 reps), hypertrophy at 65–85% (6–12 reps), and endurance at 50–65% (15+ reps). The percentage chart above shows the exact weight for each zone based on your estimated max.
RPE/RIR-based training
The modern approach prescribes RPE (rate of perceived exertion) or RIR (reps in reserve) instead of fixed percentages. For example, RPE 8 means stopping with 2 reps in reserve. This autoregulates intensity based on daily performance, sleep, recovery, and stress — more adaptive than fixed percentages which assume every session is equal.
Even with RPE-based programming, estimated 1RM remains valuable as a tracking metric. Watching your e1RM increase over time is one of the clearest indicators of strength progress. Evid calculates this automatically from every working set.
When estimated 1RM is less accurate
All three formulas hold well for 2–10 reps but break down at the extremes. Above 15 reps, fatigue factors dominate over pure strength and the relationship between weight and reps becomes less predictable. The formulas are most accurate for compound barbell movements (squat, bench press, deadlift, overhead press) and less reliable for machines and isolation exercises.
Want your 1RM tracked automatically?
Evid calculates your estimated 1RM from every working set using the Epley formula. PRs are detected automatically and tracked over time — no manual logging needed.
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