Some people have asked me the use in using a bench press calculator. This is a very simple fact. It can take the amount that you bench press and how many reps and then give you the projected one rep maximum weight you can handle. This is useful when trying to "max out" because it gives you an idea of where to start. Without using a good bench press calculator.
When trying to do your max weight rep, you need to realize it will be very tough. Try to only attempt this weight once or twice a week for best results. If you are trying every day, chances are you won't be able to hit your maximum every time.
With all that said, take this information and the link to the calculator that I posted and try it for yourself. Once you input your info, you will greatly understand how close the estimate is. It is a basic formula that is used to determine the maximum weight you "should" be able to lift. As with any of calculations of this nature, they will never be perfect. You might have some variance with what the tool tells you and what is the actual case. This is to be expected, but the results will be very close nonetheless.
For example, there is a free bench press calculator that allows you to calculate this all very easily. At that page you can figure your projected one rep max weight in a matter of 2 seconds. Take this information next time you hit the gym and try it.
Hope the tool helps and have a great workout!