One-rep Max Calculator

One-Rep Max Calculator

The one-rep max (or 1RM) is the maximum weight someone can lift in a particular exercise. It is a statistic used in weight- and power lifting which reflects the maximum strength someone can lift.

Estimation methods

There are many estimation methods to calculate the one-rep max, such as Adams', Lombardi's, Mayhew's, Brzycki's and Epley's formula (Simonsen et al., 2025). Research into the accuracy and reliability of these formulas shows that, generally, the difference between the formulas is small (Grgic et al., 2020; Wood, Maddalozze & Harter, 2002, Simonsen et al.). This Calkit calculator uses the popular Epley's formula for estimation, which has shown to be accurate, and fairly consistent across exercises (Epley, 1985; Reynold, Gordon & Robergs, 2006; Wood, Maddalozze & Harter).

Epley's formula:

Where W is the lifted weight in any unit of measurement, and r is the number of repetitions performed.

How to estimate

• Pick an exercise you would like to know your maximum weight for.
• Do a small warm-up with a low resistance.
• Have 2-3 minutes rest.
• Now, for the weight to do the estimation with, aim for a weight with which you can do approximately 5 reps. This is usually a weight around 60-80% of your estimated maximum. The formula gives you the best estimation around 5 reps, and declines in accuracy at more than 10 reps (Wood, Maddalozze & Harter, 2002; Reynold, Gordon & Robergs, 2006).
• Perform the exercise with that weight until failure and count your reps. Remember to keep proper form.
• Plug in the weight of the lifted object and your repetitions in the calculator to find out your one-rep max.

Example

Samuel is eager to know his one-rep max for his bench press. He goes to the bench press and performs a small warm-up with a light resistance. He rests for 3 minutes. He estimates that his maximum weight that he can bench is 180 lbs (~82kg). This means that he needs a weight of around 70% * 180 = 126 lbs (~57kg) to do the test with. He is able to perform 6 reps with that weight. Plugging in the values into Epley's formula gives:

1RM = 126 * (1 + 6/30) = 151.2 lbs (68.58 kg).

References

• Epley, B. (1985). Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises, 86.
• Grgic, J., Lazinica, B., Schoenfeld, B. J., & Pedisic, Z. (2020). Test–retest reliability of the one-repetition maximum (1RM) strength assessment: a systematic review. Sports medicine-open, 6(1), 1-16.
• Reynolds, J. M., Gordon, T. J., & Robergs, R. A. (2006). Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. The Journal of Strength & Conditioning Research, 20(3), 584-592.
• Simonsen, M. B., Jolas, E., Pedersen, S. R., Jensen, J. G., Faarup, M., Jakobsen, R. T., ... & Kristiansen, M. (2025). Analyzing one-repetition-max predictions: load-velocity relationship vs. repetition to failure equation in ten lower extremity exercises. Sport Sciences for Health, 21(1), 343-353.
• 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.