How to sell a product based on measurements

I am trying to figure out how to add our products and I have two issues. First is how can I set it up to sell based on 2 measurements?


20" length

20" width

Based on .08 per sq inch? I would like to get it down to the fraction if I can like we have in our current shopping cart seen here Custom Made High Quality Table Pads - Berger's Table Pads if you add a product and go though the shopping cart we need it to work something like that.

How can we do this in CS-Cart?

Any got any ideas or can make this? I need it ASAP we will pay to have this made if someone can make it. I emailed support but no reply yet if this is already an option.