When you are preparing to take on a strength training program, one of the most important variables that you will likely see on your strength training plan is the term 1RM.

Also known as one-repetition maximum for one rep max, your 1RM is an extremely useful metric that can help you determine how much weight you should be lifting for each exercise depending on the number of reps that you plan to do, or conversely, how many reps you should do with a specific weight.

But, what exactly is one rep max? How do you calculate 1 RM? Once you have numbers from a 1 RM calculator, how do you apply one-rep max to your strength training workouts?

In this article, we will discuss the significance of 1 rep max in strength training, how to calculate one RM, and how to apply the output from a 1RM calculator to your strength training workouts.

We will cover: 

Let’s dive in! 

One of the most important metrics pertinent to strength training and workout programming is your one-repetition maximum, usually referred to as your 1RM, 1 rep max, or one rep max.

As the term describes, your 1 rep max is the most you can possibly lift with proper form for one complete rep of a given exercise.

It is most commonly used for multi-joint, compound exercises such as the squat, deadlift, and bench press, though depending on the type of weightlifting workout you are doing, it may also be applied to other lifts on your strength training plan.

Rather than actually loading up a barbell with the heaviest weight you can manage for truly only one repetition, your one-rep max is typically determined by using the heaviest weight you can comfortably and safely lift for a deadlift, bench press, or squat.

You will then perform as many reps as possible with this heavy load and then use a 1RM calculator or 1RM equation to determine your 1RM or maximum strength level.

When using a 1 rep max calculator or predictive equation with this approach, it is always best to use the heaviest weights that you can manage, aiming to use a weight that you can really only handle with proper form for 3 to 4 reps. 

The accuracy of a 1 rep max calculator decreases the more the equation or 1 RM calculator has to extrapolate your 1 rep max from the work that you did. 

In other words, you will get a more accurate estimation of your actual one rep max if you are using a 1RM calculator to predict your 1RM from a weight you can lift for 3 reps versus a lighter weight you can lift for 12 reps. 

This is because the differential is much smaller when you’re predicting weight from three reps down to one rep versus 12 reps down to one rep, so there’s a narrower margin of error.

From a theoretical perspective, if you can load up a 45-pound barbell with two 20-pound plates per side and do one rep of the bench press (but not two reps), your 1RM bench press is 125 pounds.

If you can do 3 reps with 115 pounds, you can use a 1RM calculator or equation to estimate your 1RM.

If you do not have access to a 1RM calculator, you can do the math yourself using a 1RM equation.

Most of these 1RM estimation equations are named for the individual who developed the formula. There isn’t necessarily a “best“ equation for calculating 1RM. 

The general results that you will get from any of the equations should be in the same ballpark, but you might find that one seems to be more accurate than others once you actually put the results to use in your training.

Note that for all of these equations, you should be inputting the weight that you have lifted in kilograms rather than pounds, so you will need to do some conversion if you only know the weight in pounds. To convert pounds to kilograms, divide the number of pounds by 2.2.

Make sure that the number of reps that you are using is the maximum number of reps that you were able to complete with the weight.

For example, if you are doing the bench press with 165 pounds (75 kg), use the maximum number of repetitions you can perform.

Here are the different formulas you can use to calculate your 1RM. For each, we have shown an example of someone who can lift 165 pounds, or 75 kg, for the bench press for a maximum of 6 reps and is trying to estimate their one 1RM for the bench press.

Example: 75 kg x (36 / 37 – 6) = 87.1 kg or 191.6 pounds

Example: 75 kg x (1 + (0.0333 x 6) = 90 kg or 198 pounds

Example: 75 kg x (1 + (0.025 x 6)) = 86.25 kg or 190 pounds

Example: 75 kg x 60.1 = 89.7 kg or 197 pounds

Knowing your 1RM for an exercise has several practical benefits for properly programming your strength training workouts.

Your 1RM serves as a great benchmark for your fitness. 

You can periodically check your progress by seeing how much improvement you have made relative to your previous 1RM for an exercise.

For example, if you are trying to build lower-body strength, you can either directly test your 1RM or calculate your 1RM with the heaviest weights you can lift for the squat and deadlift every 4-6 weeks 

You can see how much more you can lift to assess whether your training program is actually effective based on your goals and progress. If you are not improving as much as you feel you should be, you can reevaluate your training and see where you might be falling short.

Aside from serving as a helpful fitness benchmark to assess your progress, the primary application of the 1RM in strength training is for determining how much you should be lifting for other exercises in your workouts and how many reps to do.

For example, your training program might say to perform 6 to 8 reps of deadlifts at 80% of your 1RM.

Thus, your deadlift 1RM is 200 pounds, you should lift 160 pounds for 6 to 8 repetitions.

The strength continuum provides a framework for how many reps you should perform for a given percentage of your 1RM.

According to the National Strength and Conditioning Association (NSCA), the following table shows the percentage of your 1RM you should use for the given number of reps of an exercise:

So, for example, if you want to perform 4 to 6 reps of the back squat, you should be using a weight that is 85 to 90% of your 1 rep max.

Ultimately, increasing your one rep max involves lifting incrementally heavier weights, using the principle of progressive overload, over the course of several weeks or months.

It is helpful to vary your strength training workouts using the strength training continuum.

For example, you might start by lifting a weight that is around 80% of your 1RM for 8-10 reps.

On another day in your training program, you could do sets of 6 reps with 85% of your 1RM.

As you get stronger, you can also do sets of 2-4 reps at 90-95% of your 1RM.

Periodically reassess your 1RM to make sure you are lifting the right loads in your workouts to see the gains you’re working towards.

Remember, in general, you can increase the accuracy of your output from a 1RM calculator or any of the 1 RM calculation equations by using lower rep sets. 

In other words, rather than using a weight that you can lift for 10 to 12 reps, try to use the heaviest weight that you can manage for 3 to 4 reps max. This will help you get a more accurate estimation of your true 1RM.

Here is a 1RM calculator from the National Academy of Sports Medicine (NASM).