How to calculate your weight training intensity


When starting off a weight lifting program, often the hardest part is to determine how much weight you should lift, how many sets and how many repetitions per set. This is rather complicated so I will break it down into the necessary steps to accurately predict your required weight for lifts.  To do this we must, as accurately as possible, figure out your maximum lift for one repetition: in workout lingo we call this your 1 RM. This is recommended to do as it will not only allow you to achieve your goals, but will also add a good safety margin to your workouts.  The first step will depend largely on your goals. 

What are your goals?

Answer this question first, as the training protocols are different based on your goal for the training. There are 4 main goals, strength, hypertrophy (building muscle mass),endurance and power. As power training is significantly different from the other three, I will leave it to a future article. They all require a different application of stress so I want to focus on intensity.

Strength Training

Since  goal here is to maximise your strength, the intensity must be high. 80-95 % of your 1 RM. You are aiming for 4-8 reps per set.


The goal here is to maximise muscle growth so you must have increased time under tension (TUT). This means lowering your intensity to between 70-85% and increasing reps to 8-12 repetitions per set.


The goal is to increase the anaerobic efficiency of the muscle, meaning it can work more effectively for longer. To do this we have to increase the reps to 12-25 and lower the intensity to 50-70% 1 RM.

How to figure out your 1 RM

I know this is the question you are all asking by now. The best (and safest) way to do this is use a sub-maximal test, predictive equations, and then tweak from there based on RPE (perceived effort) and actual set/rep completion. Say what you say? Let me put this in plain english. 

  1. Select a weight you think you can lift at least 3 times
  2. Perform the lift using proper technique to failure (meaning you can't do one more rep)
  3. Plug the numbers into the formula

This is the formula you would use:

1 RM = resistance used x {1 + (0.03 x repetitions performed)}

Note: There is a considerable amount of research behind this, it is accurate but not exact. The best predictability is when you do a lower number of reps (say 4-6), as the formula does not factor in stability requirements.

Let's use an example. Lets say you want to set your weight for bench press. You would then pick a reasonable weight. For me I would say 70kg. I set it up and successfully do 5 reps to failure. Now I plug into the formula:

1 RM = 70kg x {1 + (0.03 x 5)}

1 RM = 70kg x 1.15

1RM = 80.5 kg

Easy right? 

Setting your resistance

To set your resistance based on number of reps and according to your goals (see below for intensity versus reps), you simply reverse the formula:

appropriate resistance (AR) - 1RM  ÷ {1 + (0.03 x desired number of repetitions)}

Continuing with the example above, lets say my goal is hypertrophy so I want to have 12 reps of my bench press to maximise TUT. I just plug this in to the formula above:

AR = 80.5 ÷ {1 + (0.03 x 12)}

AR = 80.5 ÷1.36

AR = 59.2 but round up to 60kg

This would mean that if there is 60kg on the bar, I should be able to do 12 reps. Next step is to test this and adjust as needed. You can use the list below to help you determine if your intensity/rep range fit into your desired goal.

Repetition to Percentage of 1 RM Predictions

  • 2 reps = 95%
  • 3 reps = 92.5%
  • 4 reps = 90%
  • 5 reps = 87.5%
  • 6 reps = 85%
  • 7 reps = 82.5%
  • 8 reps = 80%
  • 9 reps = 77.5%
  • 10 reps = 75%
  • 12 reps = 70 %

Why would you bother to do this? The answer is simple. When you go to the gym, you want to maximise your results. For weight training, your goals should dictate your intensity. This is science baby. 

Did you like this article? Want to get in touch with me? I am a certified personal trainer and looking for clients like you. Drop me a line.

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