Flooring product calculator needed

[foaad]

I am a newbie in PHP and OSC. I am trying to create a calculator for Product_info page

1. where customer inputs the width and length of the area and the calculator calculates the surface area (this is the easy part).
   
2. Then the calculator will takes the result and divides it by the dynamic amount of product per case (in square foot)(it is a different value for each product) and gives the number of cases of the particular product.
   
3. In the background I need the same calculator to calculate the weigh of the cases and have a total handy when customer orders it to pass it on to shipping pages and calculate the price for shipping.
   

Any assistance would be immensely appreciated.