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One Rep Max Calculator: Figure Out Your Max Weight For any Lift


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Based on the information provided, your One Rep Max (1RM) is

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What is 1-Rep Max?

The term “one rep max” (1RM) refers to the maximum amount of weight you’re capable of lifting on a given exercise for exactly one repetition (rep). When it comes to figuring out your 1RM, the most obvious way is to simply load up the bar and see how much you’re able to lift.

However, doing so can be incredibly taxing on your body, which in addition to impinging on your long-term progress, can also increase your risk of injury.     

That’s why instead, many trainers and athletes rely on a 1-rep max calculator when it comes to designing their training programs. While it does only provide an estimate, most people will likely find that their calculations are pretty darn close.

So how is the estimate actually calculated?

The 1-Rep Max Formula

There are actually a number of different formulas for calculating your 1 rep max.   Perhaps the most accurate one, however, is the Brzycki formula, which is what we use in our calculator.   

Here’s what it looks like:

Weight lifted ÷ (1.0278 — 0.0278 x # of reps)

So here’s how it would look if you were to lift 225 for exactly 5 reps:

225 ÷ (1.0278 — 0.0278 x 5)

225 ÷ (1.0278 — 0.139)

225 ÷ 0.8888


1RM = 253 lbs

While you can technically get a 1RM estimate by inputting any given number of reps, the formula becomes less accurate the higher you go.  For the most accurate results, you’ll want to use a weight that you can only lift for 10 reps or less. In general, the closer you get to 1-rep, the more accurate the formula is going to be.

Why is Knowing Your 1-Rep Max Useful?

⫸Strength Training

Knowing your 1RM is extremely important when it comes to strength training.  In fact, in order to set up most strength training programs, you’ll not only need to know your 1-rep max but also different percentages of it.   

Take the popular 5/3/1 program for example.  In each session, you’ll be working at different percentages of your 1RM.  Here’s what it looks like:

Session 1:1 set of 5 reps at 65% 1RM, 1 set of 5 reps at 75%, and 1 set of 5+ reps at 85% 1RM

Session 2:1 set of 3 reps at 70% 1RM, 1 set of 3 reps at 80% 1RM, and 1 set of 3+ at 90% 1RM

Session 3: 1 set of 5 reps at 75% 1RM, 1 set of 3 reps at 85% 1RM, and 1 set of 1+ reps at 95% 1RM   

One of the main reasons it’s so important to know your 1-rep max when it comes to strength training is that in order to make gains, you need to be working at a high enough intensity.  

If you’ve underestimated your abilities in your programming, however, you may not be challenging yourself with enough weight to see the improvements you’re after.

⫸Progressive Overload

Knowing your 1-rep max can also be helpful when it comes to monitoring your training progress.  Even if you’re mostly interested in building muscle as opposed to strength, keeping track of your 1RM will allow you to see whether or not your training is actually paying off.  

Most hypertrophy-based training programs are based around the principle of progressive overload, which in basic terms, refers to the idea that in order to see the most gains, your training volume needs to go up over the course of your program.  

Understanding where your 1RM is at will help you to more accurately devise an approach oriented around making gradual increases in your training.  If you’re seeing that the amount of weight you’re able to lift and/or the number of reps you can do are going up, it’s a good sign that you’re on the right track.     

⫸Weight Loss

Having a reliable estimate of your 1-rep max can also be helpful when it comes to weight loss.  When most people say they want to lose weight, of course, what they really mean is that they want to shed excess body fat, not lean muscle mass.  

The only issue is that you become more susceptible to losing muscle during a hypocaloric diet.  However, hitting the weight room and keeping track of your strength is one of the best ways to make sure your targeting fat and not muscle during your weight cut.  

In general, if you’re losing weight but maintaining your strength, it’s a good sign that you’re shedding body fat, not muscle.


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