One Rep Max (1RM) Calculator

Estimate your one-rep max using seven scientifically validated formulas. Enter the weight you lifted and the number of reps you completed, and this calculator will predict the maximum weight you could lift for a single repetition. Results include a percentage-based training load table for programming your workouts.

What Is a One Rep Max (1RM)?

Your one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form. It's a fundamental measure of muscular strength used by strength coaches, personal trainers, and athletes to design training programs and track progress over time.

Directly testing your true 1RM can be risky, especially without experienced spotters and proper warm-up. This calculator provides a safer alternative by estimating your 1RM from submaximal lifts, which is the weight you can lift for multiple reps.

The Formulas

This calculator implements seven well-known 1RM prediction formulas, each developed through research on different populations and using different mathematical approaches.

Epley Formula (1985)

The Epley formula is the most widely used 1RM prediction equation. It assumes a linear relationship between weight and reps, adding approximately 3.3% to the estimated 1RM for each additional rep performed. It tends to slightly overestimate at higher rep ranges (above 10).

Brzycki Formula (1993)

Developed by Matt Brzycki, this formula is often considered the most accurate for rep ranges of 1-10. It uses a hyperbolic relationship that becomes increasingly conservative as reps increase. Many strength coaches prefer this formula for programming purposes.

Wathen Formula (1994)

The Wathen formula uses an exponential decay model and is considered one of the more accurate formulas across various rep ranges. It provides a good balance between the aggressive Epley estimate and the conservative O'Conner formula.

Lander Formula (1985)

The Lander formula uses a simple linear model. It's straightforward and provides reasonable estimates for moderate rep ranges but can become unreliable above 15 reps.

Lombardi Formula (1989)

Lombardi's formula uses a power function, which means it increases the estimated 1RM by smaller increments as reps increase. This makes it relatively conservative compared to linear formulas like Epley.

Mayhew et al. Formula (1992)

This formula was developed using data from NFL Combine testing, specifically the bench press test where players lift 225 lb for maximum reps. It may be particularly accurate for upper body pressing movements.

O'Conner et al. Formula (1989)

The O'Conner formula is the most conservative of the common 1RM equations, adding only 2.5% per rep. It's useful when you want a safer, more conservative estimate for training purposes.

Which Formula Is Most Accurate?

Research comparing these formulas shows that no single equation is universally superior. Accuracy depends on several factors including the exercise being tested, the individual's training experience, and the rep range used for the test.

General findings from the research literature:

For 1-5 reps: All formulas tend to be reasonably accurate, with differences typically under 5%. The Brzycki and Epley formulas perform well in this range.

For 6-10 reps: The Brzycki, Wathen, and Lander formulas tend to be most accurate. Epley may begin to overestimate slightly.

For 11+ reps: All formulas become less reliable. The Epley formula tends to overestimate, while Brzycki becomes mathematically unstable approaching 37 reps. Consider retesting with heavier weight if possible.

How to Use Your 1RM

Once you know your estimated 1RM, you can use percentage-based training to program your workouts for specific goals:

Strength (85-95% 1RM): Heavy loads with low reps (1-5) develop maximal strength by training your nervous system to recruit more muscle fibers and improving intermuscular coordination.

Power (75-85% 1RM): Moderate-heavy loads moved explosively develop power—the ability to generate force quickly. This range is popular in athletic training programs.

Hypertrophy (65-80% 1RM): Moderate loads with moderate reps (6-12) are most effective for building muscle size through mechanical tension and metabolic stress.

Muscular Endurance (50-65% 1RM): Lighter loads with higher reps (15+) improve the muscles' ability to perform repeated contractions over time.

Tips for Accurate Testing

To get the most accurate 1RM estimate from this calculator:

Use 3-7 reps when possible. This rep range provides the best balance of accuracy and safety. Single reps are accurate but risky; very high reps reduce prediction accuracy.

Choose an appropriate weight. Select a weight that brings you close to failure at your target rep range. If you could easily do more reps, the estimate will be less accurate.

Use good form throughout. Reps performed with poor form or excessive momentum shouldn't count toward your test set.

Be well-rested. Fatigue from previous sets or workouts will reduce your performance and skew the results. Test after adequate warm-up but before fatigue accumulates.

Retest periodically. As your strength changes, so does your 1RM. Retest every 4-8 weeks or when changing training programs to keep your percentages accurate.

References:

1. Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985.
2. Brzycki M. Strength testing—predicting a one-rep max from reps-to-fatigue. J Phys Educ Recreat Dance. 1993;64(1):88-90. https://doi.org/10.1080/07303084.1993.10606684
3. Lombardi VP. Beginning Weight Training: The Safe and Effective Way. Dubuque, IA: Wm. C. Brown; 1989.
4. Mayhew JL, Ball TE, Arnold MD, Bowen JC. Relative muscular endurance performance as a predictor of bench press strength in college men and women. J Appl Sport Sci Res. 1992;6(4):200-206.
5. O'Conner B, Simmons J, O'Shea P. Weight Training Today. St. Paul, MN: West Publishing; 1989.
6. Wathen D. Load assignment. In: Baechle TR, ed. Essentials of Strength Training and Conditioning. Champaign, IL: Human Kinetics; 1994:435-446.
7. Lander J. Maximum based on reps. Natl Strength Cond Assoc J. 1985;6(6):60-61.
8. LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res. 1997;11(4):211-213. https://pubmed.ncbi.nlm.nih.gov/12426614/
9. Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. J Strength Cond Res. 2006;20(3):584-592. https://pubmed.ncbi.nlm.nih.gov/16937972/