One-Rep Max (1RM)

This calculator takes two inputs — the weight you lifted and the number of repetitions you completed — and applies two industry-standard formulas (Epley and Brzycki) to estimate your true one-rep max. Rather than requiring you to attempt a dangerous all-out single, it extrapolates from a working set you performed with good form, typically in the 3–10 rep range. Both formulas are well-validated in exercise science literature and tend to produce closely aligned results when reps stay below 10, giving you a reliable estimate you can act on immediately.

The Epley formula, developed by Boyd Epley at the University of Nebraska, calculates 1RM as: weight × (1 + reps / 30). The Brzycki formula, created by Matt Brzycki, uses a slightly different model: weight × 36 / (37 − reps). At low rep counts (3–5 reps), these two formulas are nearly identical. As the rep count climbs toward 10 or more, they can diverge slightly, which is why the calculator displays both — letting you see a realistic range rather than a single potentially overconfident number. Most serious lifters use the average of the two or lean on the more conservative figure when setting training loads.

Once your estimated 1RM is established, the calculator generates a percentage-based training table, typically showing loads at 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95% of your 1RM. These percentages map directly onto standard periodization schemes: lower percentages (50–65%) correspond to speed and technique work, mid-range percentages (70–80%) are the bread-and-butter hypertrophy and strength-endurance zone, and higher percentages (85–95%) drive maximal strength adaptation. Using this table, you can translate an abstract 1RM number into the exact plates to load for every session in your program.

The most important factor affecting the accuracy of your 1RM estimate is the rep range you use as your input. Research consistently shows that estimates derived from sets of 3–6 reps are more accurate than those from sets of 10 or more, because fatigue, cardiovascular limit, and muscular endurance start to influence performance at higher reps, making the extrapolation less precise. A common mistake is plugging in a set performed to absolute failure with poor form — the last reps may not represent true strength capacity. For best results, use a set where you completed the target reps with one or two reps still in reserve, and test the same exercise consistently to track progress over time.