# Formula for Rep max?

I can find 1 rep max using Brzycki but I'm not able to find other values greater than 10 rep max. How can I find more than 10 rep max values; are there any formulas? In the above image they are calculating until 20 rep max. How can I calculate 20 rep max and above. Are there any formulas?

• At what number of reps do you think such a formula would stop working? Aug 15, 2020 at 20:28
• It will be based on the weight Aug 16, 2020 at 16:15
• Weight is the variable here, so I don't know what you mean. My question was intended to get you to consider the fact that any formula has to stop working at some number of reps, and from that to realize that 1RM calculations are by their very nature not going to work well at extrapolating 1RM from high rep maxes. So while you can make a formula that gives a predicted 1RM from your 20RM, it isn't going to be very useful. Aug 18, 2020 at 6:59

There is a handful of "accepted" formulae to calculate one's 1RM based on other xRMs. In fact, there's a nice Wikipedia article that lists them: https://en.wikipedia.org/wiki/One-repetition_maximum#Calculating_1RM

But in all cases, you have to keep in mind that there doesn't exist a single formula that could perfectly predict any person's 1RM given submaximal testing. There are too many variables at play between different people, and all these formulae only consider the results of one submaximal test.

Additionally, it is understood that all of these estimations get worse and worse the higher you take your repetitions in your test. Testing your 20RM is always going to give a much more volatile estimate than if you did a 3RM or 5RM because higher reps involve more muscular stamina, which isn't an inherent factor in the formula.

Furthermore, these tests are more suited for those who have trained for a while, because rookie lifters might be able to crank out 20 reps of low weight, but they haven't prepared their nervous system to even hold the weight of their estimated 1RM.

The same formulae can be used to estimate other xRMs too. To do so, you need to isolate the weight variable in the equations instead of the 1RM variable.

Here's an example using the Lombardi formula.

Originally, the equation states:

``````1RM = wr^(0.10)
``````

Isolating the `w` variable we instead get

``````w = 1RM / (r^(0.10))
``````

For this example, let's say your 1RM is 100kg, and you want to estimate your 20RM. We would insert `1RM = 100`, `r=20`, and isolate `w`, giving us

``````w = 100 / (20^(0.10)) ~ 74.11kg
``````
• Thanks for your answer, Actually I can find 1Rm to 12Rm but what I'm asking is how can I find till 20Rm?.... I know 20Rm would not be accurate but anyhow I need it Aug 16, 2020 at 16:14
• @SURYA - I've added a section to my answer explaining how you can use the same formulae to do so.
– Alec
Aug 16, 2020 at 16:27
• @SURYA Why do you need it? Aug 18, 2020 at 6:59