Health & Medicine · Fitness
One Rep Max Calculator
Calculate your one-repetition maximum (1RM) for any lift using weight lifted and number of reps performed, based on the Epley, Brzycki, and Lander formulas.
Calculator
Formula
w is the weight lifted in pounds or kilograms, and r is the number of repetitions performed. The Epley formula estimates the theoretical one-repetition maximum. The Brzycki formula uses 1RM = w × (36 / (37 − r)) for an alternative estimate.
Source: Epley, B. (1985). Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises. Brzycki, M. (1993). Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance, 64(1), 88–90.
How it works
The Epley formula, developed by Boyd Epley in 1985, is one of the most widely used 1RM prediction equations in strength training. It calculates your estimated max as the weight lifted multiplied by the quantity (1 + repetitions divided by 30). The formula performs well across a moderate rep range of 2–10 reps and is commonly implemented in gym software and fitness apps worldwide.
The Brzycki formula, published by Matt Brzycki in 1993, provides a slightly different estimate using the equation: 1RM = weight × (36 / (37 − reps)). This formula is particularly accurate for lower rep ranges (1–10 reps) but becomes mathematically undefined at or above 37 repetitions. Many coaches favor Brzycki for powerlifting-style assessments because it is slightly more conservative than Epley for sets in the 1–5 rep range.
The Lander formula uses a regression-based approach: 1RM = weight / (1.013 − 0.0267123 × reps). This formula was validated against actual 1RM performance data and tends to produce estimates that closely track both Epley and Brzycki results for typical training rep ranges. By averaging all three formulas, this calculator reduces the impact of any single equation's bias and gives you a more robust central estimate of your true maximum strength. The percentage outputs (70%–90% of 1RM) help you immediately apply your result to common training programs such as powerlifting periodization, hypertrophy blocks, and strength-endurance work.
Worked example
Suppose an athlete performs 5 repetitions with 225 lbs on the bench press. We apply each formula:
Epley: 225 × (1 + 5/30) = 225 × 1.1667 = 262.5 lbs
Brzycki: 225 × (36 / (37 − 5)) = 225 × (36 / 32) = 225 × 1.125 = 253.1 lbs
Lander: 225 / (1.013 − 0.0267123 × 5) = 225 / (1.013 − 0.1336) = 225 / 0.8794 = 255.9 lbs
Average estimate: (262.5 + 253.1 + 255.9) / 3 = 257.2 lbs
This means the athlete can program their bench press training using approximately 219 lbs (85%) for strength work, 206 lbs (80%) for hypertrophy, and 180 lbs (70%) for endurance-focused accessory work.
Limitations & notes
Predictive 1RM formulas are estimates, not exact measurements, and their accuracy decreases significantly as the number of repetitions increases beyond 10. Sets performed at very high rep ranges (15+ reps) reflect muscular endurance far more than maximal strength, and applying these formulas in that range typically overestimates the true 1RM. These formulas also assume that the set was performed to muscular failure or near-failure with proper technique — a conservative submaximal set will underpredict your actual maximum. Individual factors such as fiber type distribution, neuromuscular efficiency, training age, and fatigue state all influence how well a submaximal set predicts a true maximum effort. Always consult a certified strength and conditioning specialist before attempting maximal lifts, particularly for beginners or athletes returning from injury.
Frequently asked questions
Which 1RM formula is the most accurate?
Research suggests that no single formula is universally superior — accuracy varies by individual, lift, and rep range. For rep ranges of 1–5, Brzycki tends to be slightly more accurate; for ranges of 6–10, Epley performs well. Using the average of multiple formulas, as this calculator does, generally reduces prediction error and gives a more reliable central estimate.
How many reps should I use to get the most accurate 1RM prediction?
The most accurate predictions come from sets of 2–5 repetitions performed at or near failure with good form. As the rep count increases beyond 10, prediction accuracy drops meaningfully because the relationship between submaximal endurance performance and true maximum strength becomes less direct. If possible, use a challenging weight that limits you to 3–6 clean repetitions.
Can I use this calculator for any exercise?
Yes — these formulas are mathematically exercise-agnostic and can be applied to any barbell lift such as squat, bench press, deadlift, overhead press, or row. However, they are less commonly validated for machine-based or single-joint exercises, where strength curves, muscle recruitment patterns, and fatigue profiles differ significantly from free-weight compound movements.
Should I test my actual 1RM instead of estimating it?
For experienced, well-coached athletes in powerlifting or strength sports, a true 1RM test under supervision is the gold standard for competition preparation. However, direct 1RM testing carries a meaningful injury risk — particularly for beginners, older adults, or those returning from injury — making submaximal estimation a safer and often sufficient alternative for programming purposes.
How do I use my 1RM to structure my training?
Your estimated 1RM is the foundation of percentage-based programming. Classic strength programs (like 5/3/1 and Westside Barbell) prescribe work sets at specific percentages of your 1RM: roughly 85–95% for maximal strength, 70–85% for hypertrophy, and 50–70% for speed and technique work. The percentage outputs in this calculator give you those training weights immediately so you can plug them directly into your program.
Last updated: 2025-01-15 · Formula verified against primary sources.