One Rep Max Calculator
Enter the weight you lifted and how many reps you completed. We'll calculate your estimated 1RM and your full training zone breakdown.
Works best with 1–10 reps. Accuracy decreases above 10 reps.
Quick Answer
One rep max (1RM) formula: Epley — weight × (1 + reps ÷ 30). For bench press: 100kg × 5 reps = estimated 1RM of ~117kg. For hypertrophy, train at 70–80% of 1RM for 8–12 reps. For strength, train at 85–95% for 3–5 reps.
What Is One Rep Max and Why Does It Matter?
Your one rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It is the universal currency of strength training — the number that lets you set precise training loads, objectively measure progress, and compare your strength to established standards. Every elite powerlifter, Olympic weightlifter, and strength coach uses 1RM as the foundation of their programming.
Beyond competitive sport, knowing your 1RM matters for a straightforward reason: training at the wrong percentage of your maximum produces the wrong adaptation. Someone trying to build muscle who trains with weights that are too light (below 65% of 1RM) will develop endurance, not size. Someone training above 90% constantly risks overtraining and injury without allowing sufficient recovery. Percentage-based training — anchored by your 1RM — removes the guesswork.
How the Calculator Works
Rather than relying on a single formula, our calculator averages three validated approaches. The Epley formula (1RM = weight × (1 + reps/30)) is the most widely used and referenced in sports science literature. The Brzycki formula (1RM = weight × 36/(37 − reps)) is more accurate for very low rep ranges of 1–5. The Lander formula provides a third independent estimate. Averaging the three reduces the error of any single formula and produces a more reliable estimate across the full rep range.
All formulas perform best when reps are in the 1–10 range. Above 10 reps, fatigue, breathing patterns, and technique breakdown introduce significant error. A set of 3–5 reps taken close to failure gives the most accurate 1RM estimate — and is also significantly safer than attempting a true maximal single.
Training Zone Breakdown: How to Use Your 1RM
Once you know your 1RM, you can structure every training session with precision. The key zones are: 90–100% of 1RM for maximum strength (1–3 reps per set), 80–90% for strength and power development (3–6 reps), 70–80% for hypertrophy or muscle growth (8–12 reps, the most well-researched range for increasing muscle cross-sectional area), and 60–70% for muscular endurance (12–20 reps). Most recreational lifters benefit most from spending the majority of training in the 75–85% range, which builds both strength and size simultaneously.
How to Build Your 1RM Over Time
The most sustainable approach to increasing your 1RM is progressive overload — consistently adding small amounts of weight or reps over time. Rather than attempting a true 1RM frequently (which is taxing and carries injury risk), track your best performance at a given rep range. When you can complete 5 reps at a given weight for 3 sets with good form, add 2.5kg (upper body) or 5kg (lower body) and begin again. Recalculate your estimated 1RM every 6–8 weeks to update your training percentages as you get stronger.
Safety note
Never attempt a true 1RM without a spotter or safety equipment, and only after a thorough warm-up. For most people, using this calculator with a 3–5 rep effort is safer and produces equally useful data.