Gym Log

One-rep max calculator.

Estimate the heaviest weight you could lift for one repetition from a completed set. The calculator shows a conventional set of seven classical formulas side by side because each method makes different assumptions and none is universally correct for every lift or lifter.

Enter a completed set

Use a continuous set completed to muscular failure or very close to failure, with consistent technique and range of motion. The equations work the same whether your weight is in kilograms or pounds.

Enter a positive number. Use a period for decimals.

Whole numbers from 1 through 20. If you are very certain of your reps in reserve, you can add them to the completed repetitions; otherwise, leave them out.

All seven estimates remain visible below.

How the calculation works

A one-repetition maximum, usually written as 1RM, is the greatest load completed once under a defined technique and range of motion. An estimated 1RM uses the weight and repetition count from a lighter set as inputs to a prediction equation.

Every method on this page returns the entered weight when the set contains one repetition. For sets of two to 20 repetitions, each formula applies its own relationship between repetitions and the percentage of maximal strength represented by the set.

Worked example

For a weight of 100 completed for five repetitions, Epley calculates 100 × (1 + 0.0333 × 5) = 116.65

Why the range matters

The formulas produce different values because they were developed in different contexts. Showing the spread makes that uncertainty visible rather than hiding it behind a single unexplained number.

Use one method consistently for trends

Switching formulas can create an apparent increase or decrease even when the underlying set has not changed. For progress tracking, consistency is generally more useful than chasing whichever method produces the largest estimate.

Formulas and original sources

Each formula is shown with its original-source citation.

Epley

1RM = w × (1 + 0.0333r)
Epley, B. (1985). Poundage Chart. Lincoln, Nebraska: Boyd Epley Workout.

Brzycki

1RM = w ÷ (1.0278 − 0.0278r)
Brzycki, M. (1993). Strength Testing: Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance, 64(1), 88–90.

Lander

1RM = 100w ÷ (101.3 − 2.67123r)
Lander, J. (1985). Maximums Based on Reps. National Strength & Conditioning Association Journal, 6, 60–61.

Lombardi

1RM = w × r0.10
Lombardi, V. P. (1989). Appendix. In Beginning Weight Training: The Safe and Effective Way (pp. 201–204). Dubuque, Iowa: Wm. C. Brown. ISBN 0-697-05496-9.

Mayhew

1RM = 100w ÷ (52.2 + 41.9e−0.055r)
Mayhew, J. L., Ball, T. E., Arnold, M. D., & Bowen, J. C. (1992). Relative Muscular Endurance Performance as a Predictor of Bench Press Strength in College Men and Women. Journal of Applied Sport Science Research, 6(4), 200–206.

O’Connor

1RM = w × (1 + 0.025r)
O’Connor, B., Simmons, J., & O’Shea, P. (1989). Weight Training Today. St. Paul, Minnesota: West.

Wathen

1RM = 100w ÷ (48.8 + 53.8e−0.075r)
Wathen, D. (1994). Load Assignment. In T. R. Baechle (Ed.), Essentials of Strength Training and Conditioning (pp. 435–446). Champaign, Illinois: Human Kinetics. ISBN 0-87322-694-1.

Limitations and interpretation

These formulas are population-derived or coach-derived estimates. Their accuracy and bias are not identical across exercises, populations, techniques, or repetition ranges. Comparative studies have reported meaningful differences by lift and by the number of repetitions completed, which is why this calculator does not declare a universal winner. 1 2

A lower-repetition set generally provides a more defensible basis for estimating maximal strength than a high-repetition set. In one study of bench press and leg press, five-repetition data produced stronger predictions than 10- or 20-repetition data, and the authors cautioned against using more than 10 repetitions in linear equations for those exercises. 3

  • Exercise matters. A formula developed or evaluated with bench press data may behave differently for a squat, deadlift, machine exercise, or isolation movement.
  • Set quality matters. Technique, range of motion, fatigue, rest, and how close the set came to failure all affect the relationship between repetitions and maximal strength.
  • Trends are more useful when the method stays fixed. Compare like with like: the same exercise, similar technique, and the same estimation formula.
  • An estimate is not an instruction. Do not treat the output as a guarantee that the weight can or should be attempted.

Supporting references

  1. LeSuer, D. A., McCormick, J. H., Mayhew, J. L., Wasserstein, R. L., & Arnold, M. D. (1997). The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift. Journal of Strength and Conditioning Research, 11(4), 211–213. DOI record
  2. Wood, T. M., Maddalozzo, G. F., & Harter, R. A. (2002). Accuracy of Seven Equations for Predicting 1-RM Performance of Apparently Healthy, Sedentary Older Adults. Measurement in Physical Education and Exercise Science, 6(2), 67–94. DOI record
  3. Reynolds, J. M., Gordon, T. J., & Robergs, R. A. (2006). Prediction of One Repetition Maximum Strength From Multiple Repetition Maximum Testing and Anthropometry. Journal of Strength and Conditioning Research, 20(3), 584–592. DOI record