Apparently doing grip exercises at 30% of maximum might reduce blood pressure.

http://www.medicalnewstoday.com/articles/14556.php

However, can you determine maximum w/o a grip dynamometer? I’ve heard with bench presses, you can determine your one rep maximum because a person can do 10 reps if the weight is 70% of their 1 rep maximum. So if your 1 rep maximum is 300 pounds, you should be able to do 10 reps at 210 pounds. Does this formula work, and can it be extrapolated downwards to 30% or 50% of one rep maximum?

Supposedly average grip strength for a man in his 20s or 30s is about 120 lbs.

http://www.pinchgauge.com/pdf/grip1.pdf

However I am more muscular than average, so mine will likely be higher, maybe 140 pounds. I really don’t know. But I’m guessing that is a rough estimate for what mine would be.

I figure after I find the 1 rep maximum, I could get a gripper that tells you in pounds or kg what kind of resistance it has.

Or would just assuming 40 pounds is a rough estimate of 30% of my maximum be the best way to go? If I do 110 pounds, that is 33 pounds. If I do 150 pounds, that is 45 pounds. Either way, 40 pounds (which is 133 pounds maximum) sounds like a good estimate of 30% of 1 rep maximum.