One-Rep Max (One-RM) Calculator

One-Rep Max Calculator

Have you ever been standing in the gym with an exercise in front of you and wondered where to even begin? What weight should I be attempting for the repetitions I have been given?

This is where a One Rep Max Calculator can help!

The 1RM is defined as the maximum amount of weight you can lift for one repetition using proper form and is considered a gold standard test outside of a lab. However, it is not always suitable for everyone to perform and the risk to rewarded ratio may be unbalanced (1).

What Is A One Rep Max Calculator?

The One Rep Max (1RM) Calculator is an extremely useful tool for everyone, from the most advanced lifters and gym users to the absolute beginner. Knowing your capabilities will not only improve your performance, but it will reduce the risk of going too heavy or too light with your weight selection (2).

A One Rep Max calculator will prevent you from training with a lack of intensity or effort. The figures give you the accountability you need to maintain the right level of intensity for your body.

When you know your 1RM, you can choose the correct weight intensity for the repetition range that matches your goal, whether it be to improve your muscular endurance, build muscle, or gain strength. You can also re-test yourself regularly to check your progress. Each exercise will have a different 1RM – they are not interchangeable.

When you use the right weights for your body during each session, you can exercise safely and effectively that will challenge you enough to get the results you want, without the worry of injury. Most gym users will not attempt a ‘true’ 1 Rep Max, but will instead perform a sub-maximal test of multiple repetitions with lighter weights. This is still an accurate measure of your current strength (3).

How Does This Calculator Work?

One of the major benefits of this 1RM calculator is that you can use it to fit the information you require or adapt it to the specific person using it.

Unless you know your actual 1RM you can lift for an exercise, we can use the other fields within the calculator and work backwards.

For example, if you enter your 3 rep max or 8 rep max it will give you an estimate of your 1 rep max. Remember, the calculator uses estimates and users who are more resistance-trained may be able to exceed their estimated 1 rep max (4).

How Is One Rep Max Calculated?

The most common scenario we see is that you are given a set repetition range to work towards, for example, 5, 8, 10 reps etc. Now let’s say you’re using the bench press exercise.

If you have programmed 10 repetitions for the bench press, basically you are being asked to perform 75% of your 1RM.

Let’s say you currently don’t know what your 1RM weight is for the bench press, this is where the calculator can help.

For example, you know you can lift 70kg for 6 reps on the bench press. In the repetition relationship table below, it shows what each repetition range is meant to represent as a percentage of intensity. 6 reps equate to working at 85% of your 1RM (100%).

  1. Now, try this calculation to find the estimated 10 rep max (75%).
  2. 70kg divided by 0.85 estimates your 1RM (100%) to be 82kg.
  3. Now let’s use this to calculate your 10 rep max which is 75%.
  4. 82kg x 0.75 estimates your 10 rep max to be 62kg.

Percentage – Repetition Relationship

REPS                       %1RM

1                              100

2                              95

3                              93

4                              90

5                              87

6                              85

7                              83

8                              80

9                              77

10                            75

11                            73

12                            70

The 1RM calculator can only provide you with an estimate. The lower the rep count, the more accurate the guess (5). For instance, if you provide the weight you can lift for 5 reps, you will get a more accurate 1RM figure than if you only provide what you can do for 12 reps.

If you want to improve your fitness, build muscle and strength then Jonple’s science and technology can help you finally reach your goals.


1. Desgorces FD, Berthelot G, Dietrich G, Testa MS. Local muscular endurance and prediction of 1 repetition maximum for bench in 4 athletic populations. J Strength Cond Res. 2010;24(2):394-400.


2. Travis Triplett. Essentials of Strength Training and Conditioning. Fourth edition. Champaign, IL: Human Kinetics, 2016. Book.

3. Hoeger, W., Barette S. L., Hale D. F., & Hopkins D. R. Relationship between repetitions and selected percentages of one repetition maximum. Journal of Applied Sport Science Research 1, (1987): 11-13.


4. Hoeger, Werner W. K. et al. “Relationship between Repetitions and Selected percentages of One Repetition Maximum: A Comparison between Untrained and Trained Males and Females.” Journal of Strength and Conditioning Research 4 (1990): 47–54.


5. MORALES, J,ANDS. SOBONYA. Use of submaximal repetition test for predicting 1RM in class athletes. J. Strength Cond. Res.10 (1996): 186, 189.


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