One Rep Max Calculator
Estimate your true one-rep max from any working set, with a training zone breakdown.
One Rep Max Calculator
Epley formula — estimate your true strength
* Most accurate for sets of 1–10 reps taken close to failure
Understanding Your Results
Your estimated 1RM is the heaviest weight you could theoretically lift for a single rep, calculated from a lighter set using the Epley formula — without the injury risk of actually testing a true single-rep max without a spotter or safety equipment.
The training zones translate that number into weights you can actually program. Lower reps at higher percentages build maximal strength and neural efficiency; moderate reps at moderate percentages — the hypertrophy zone — is where most visible muscle growth happens; higher reps at lower percentages build the muscular endurance that keeps form solid late into a workout.
This number isn't fixed — it moves as you get stronger, and it can also dip with poor sleep, high stress, or being under-fueled. Use it as a training guide and re-test every few weeks rather than treating one calculation as permanent.
Accuracy depends on how close your input set was to true failure. If you stopped with several reps left, your estimate will run higher than your real capability — for the most useful number, use a set where the last 1–2 reps were genuinely difficult.
Frequently Asked Questions
The Epley formula (weight × (1 + reps/30)) estimates your one-rep max from a lighter, safer set instead of requiring you to actually attempt a maximal single lift, which carries higher injury risk, especially without a spotter. It is most accurate when your set is taken close to failure, with 1–10 reps.
It is generally within 5–10% of your true 1RM when the input set is taken close to muscular failure. Accuracy drops the further you get from failure (if you stopped a set with several reps left in the tank) or the higher the rep count goes beyond 10–12 reps.
They translate your estimated max into practical training weights — the strength zone (90%, ~3 reps) builds maximal force production, the hypertrophy zone (75%, ~10 reps) is the classic muscle-building range, and the endurance zone (65%, ~15 reps) builds muscular stamina. Pick the zone that matches your current training goal.
Beginners can use estimated 1RM as a rough guide, but should prioritise learning correct form at lighter weights before chasing percentage-based programming. Re-test every 4–6 weeks as strength improves rather than assuming a single number stays accurate for months.
Epley's formula was developed primarily around barbell compound lifts like the squat, bench press, and deadlift, where it is most reliable. It becomes less reliable for isolation exercises or movements with a strong stability or skill component, like Olympic lifts.
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