One Rep Max (1RM) Calculator — Epley & Brzycki

A one rep max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is the gold standard for measuring absolute strength in powerlifting and strength training. Knowing your 1RM lets you set precise training percentages for programming (e.g., 80% of 1RM for 5 sets of 3 reps).

No single formula is universally most accurate — results depend on the individual, exercise, and rep range. The Epley and Brzycki formulas are the most widely used and perform best in the 2–10 rep range. Brzycki tends to give lower estimates while Epley gives slightly higher ones. Using the average of multiple formulas (as shown in this calculator) typically reduces individual formula error. For reps above 10, accuracy decreases significantly for all formulas.

Training programs prescribe loads as percentages of your 1RM. The NSCA textbook (Essentials of Strength Training and Conditioning) uses these ranges: 85% of 1RM or more for maximal strength (up to 6 reps), 67–85% for hypertrophy (6–12 reps) and 67% or less for muscular endurance (12 reps or more). The rep percentage chart in this calculator shows estimated weights for 2–12 reps based on your average 1RM.

Testing your true 1RM carries injury risk, especially for beginners and for exercises like squats and deadlifts. A submaximal estimation (performing a set of 2–5 reps with a challenging weight and using a formula) is safer and nearly as accurate for programming purposes. Always warm up thoroughly, use a spotter for upper-body lifts, and consider estimated 1RM testing rather than true maximal lifting.

Yes, the formulas are exercise-agnostic — you can use them for any barbell exercise: bench press, squat, deadlift, overhead press, barbell row, etc. However, the accuracy varies: formulas are most accurate for compound lifts tested in the 2–6 rep range. For isolation exercises or higher rep sets (above 10), the estimates become less reliable.

The Epley formula (Epley, 1985) is the most widely used 1RM estimation formula: 1RM = weight × (1 + reps/30). It was one of the first published 1RM prediction equations and remains popular due to its simplicity and reasonable accuracy across a variety of rep ranges. Below 10 reps it gives slightly higher estimates than Brzycki.