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One rep max (1RM) calculator

What is a one rep max?

One repetition maximum, often called simply one rep max or 1RM, refers to the maximum amount of resistance (usually measured as weight) that an individual can generate sufficient force against in order to successfully complete one repetition of an exercise.

Whilst any resistance training exercise can be tested for your one repetition maximum, it’s most useful for compound exercises, such as the bench press, deadlift or squat.

For example, an individual may be able to bench press a maximum of 100 kilograms for one repetition, but no more than that. That would make 100 kilograms their current one repetition maximum.

One repetition maximum is a commonly used measure of muscular strength.

Many strength training programs use percentages of one repetition maximum to indicate the desired exercise difficulty. For example, a workout session may include three sets of ten repetitions on bench press at 75% of your one repetition maximum.

Predicting one repetition maximum using submaximal estimation

An individual’s one repetition maximum for an exercise can be calculated indirectly using submaximal estimation.

To do this, the person (or their fitness trainer) would select a weight that they believe they could complete 5 or 6 repetitions of the exercise with, whilst maintaining correct form (exercise technique) throughout all repetitions. Once the exercise is completed, the person (or fitness trainer) would then record the number of repetitions and use a calculation (or our handy calculator!) to predict the person’s one repetition maximum.

Submaximal estimation of an individual’s one repetition maximum is typically less accurate when calculated from a higher number of repetitions. For example, calculating one repetition maximum from 12 repetitions of a barbell back squat will be less accurate than using a lower number of repetitions, such as 6, at a higher level of resistance (i.e. heavier weight).

It’s best to keep the number of repetitions below 11. For more advanced participants, the number of repetitions could be as low as 3.

The submaximal estimation method has some advantages over direct maximal testing, including:

  • submaximal loads are safer to lift, particularly for beginners;
  • it’s much quicker, as direct testing of one repetition maximum typically involves a lot of trial and error; and
  • it’s less unnerving for inexperienced weight lifters.

However, it’s important to remember that it’s just an estimation; and the results of this calculation will not be as accurate as direct maximal testing.

One Rep Max Calculator

How submaximal estimation is calculated

The calculation for submaximal estimation of one repetition maximum is:

( (weight lifted x 0.03) x number of repetitions ) + weight lifted = 1RM

Calculation from: Essential Guide to Fitness for the Fitness Instructor, Rosemary Marchese, 2016.

For example, if an individual was able to complete six repetitions at 40kg, the calculation would be:

( (40kg x 0.03) x 6 repetitions ) + 40kg = 47.2kg

Training program considerations

If you wish to develop a training program for yourself or for a client using one repetition maximum percentages, then the Repetition Continuum table below should be very helpful!

Repetition Continuum: One Repetition Maximum

Table adapted from: Essential Guide to Fitness for the Fitness Instructor, Rosemary Marchese, 2016.

Article image credit: Matt Madd, Flickr.

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Fitness Instructor and qualified cook. Passionate about strength training and healthy eating.

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