I have problem with product page.

I'm working with products with prices depend from meters^2, so I prepared rule to calculate this price. Actually, client can give width and lenght and he should get calculated price, but it works only after clicked "Add to cart". How can I do to dynamicly calculation price before "Add to cart" click? I try with Commerce Product Attributes but it doesnt work with text input fields (or maybe I couldnt use this) .

Please help me.