Here's how to find out your 1 rep bench press max based on your 10 rep max.
A team of graduate students, getting their Phd in exercise physiology, at a local university working in conjunction with local bodybuilders and powerlifters developed the following formula. It's really incredible how accurate it is. Try it on yourself.
Let's say a person can do 315 for 10 reps.
Take the 315 and subtract the waist circumference. Let's say that's 38.
then take that number and subtract the person's age. Let's say that's 30.
then take that number and add 12% of their bodyweight weight. let's say they weigh 235.
take that number and subtract their arm length, both arms from shoulder cap to wrist bone. Let's say that's 23" for each arm=46
take that number and multiply it by the number of reps they did at 315, which is 10.
take that number and multiply it by the number of reps they can get 30 reps with, let's say that's 225.
then take the square root of that number.
And next divide that number by 1.459
In this case, the person's 1 rep max would theoretically be 491.98 pounds. This formula is incredibly accurate in the real world.
Let's take one more example with a different person:
Let's say this person can do 275 for 10 reps.
Take the 275 and subtract the waist circumference. Let's say that's 34.
then take that number and subtract their age. Let's say that's 24.
then take that number and add 12% of their weight. Let's say they weigh 205.
take that number and subtract their arm length, both arms from shoulder cap to wrist bone. Let's say that's 22" for each arm=44
take that number and multiply it by the number of reps they did at 275, which is 10.
take that number and multiply it by the number of reps they can get 30 reps with, let's say that's 175.
then take the square root of that number.
And next divide that number by 1.459
In this second case, the person's 1 rep max would theoretically be 403.45 pounds.
Give it a try and see how accurate it is. You do have to remember this formula only works with people experienced with weight training. It is not applicable to an untrained person or somebody in their first week back after a year layoff.
MaxRep