here is how you calculate what you can max.
what weight can you benchpress ten times with perfect form? This weight is 70% of what you could max...
say for example, I can benchpress 235 10 times roughly on a good day

. So take 235 and multiply it by 130%, or 1.3, and that gives you an estimate of what you should be able to max. which for me.. it comes out to 305.5 lbs. 305.5 multiplied by .7 (70%) will take you back down to your original number of 235.
If you've never max'ed before... make sure you have a spotter. Make sure you've had plenty of rest, and that you give your entire body 2 days rest AT LEAST before you max out the chest. You need all those stationary muscles ready to help.
Warm up with a nice light weight 4 to 5 times..
then add 20 to 30 lbs, do 2 reps
20 to 30 lbs, 1 rep
more weight if necessary, 1 rep.
a little more weight, 1 rep.
do this until you reach your max. the whole point is to NOT tire yourself out before you reach the max. so if you've never max'ed before... take my advice. if you have max'ed before... you know all this already i assume
best of luck to you