surface calculation

Hi,

Please provide more information, like an example with a product, so that we can better understand what you're trying to achieve.

Hi,

Ok, I see.
There is no such system. That would require some customization.
I would recommend adding that surface input directly to the filter view file, developing a small hikashop plugin to add a filter on the products if necessary (it doesn't actually seem to filter anything as I still see all the products on that link), and customize the product display block (listing_img_title, or listing_img_desc view file) to take the value entered in the input for the display of the prices of the products.
If you're not a developer yourself, you can contact our partners for such custom job:
www.hikashop.com/home/our-partners.html