1. Mix the concrete according to the manufacturers instructions. Different mixes require different materials be added in specific quantities to achieve the desired consistency and
http://www.ehow.com/how_8040919_calculateconcrete...

by using pythagoras therom and using the the cosine rule pounds per square inch is really the result of an elephant.
http://wiki.answers.com/Q/How_do_you_calculate_psi

Formula for calculating PSI: Force = Area * Pressure. May I assist you further?
http://www.chacha.com/question/whatistheformula...

As long as the amount of air has not changed, and neither did the Temperature, then the pressure inside the structure is inversely proportional to the volume of the structure, or:
http://answers.yahoo.com/question/index?qid=201309...
