Calculating one rep max from reps

[training700]

How was it developed anybody have an idea how it's supposed to calculate right.
I've always wondered because it never works for me. from a double i can usually jump a significant more amount than it says should and way more than a triple.

 

[joeblow12345]

The calculator is bs. Dont believe it unless you wanna look foolish when you attempt your projected max and fail miserably. Its a general guideline and I wouldnt treat it as anything else. In order to lift a max weight your body has to be conditioned to handle the load. There is very little room for error with max weights as well. Your max is the weight that you can do 1 time by yourself, not with a spotter holding the bar. Go find your max and base your percentages off of it.

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[training700]

It's opposite for me based off reps shouldn't be able even come close to my real max, but i do train a lot for one reps.