Drupal commerce: product field based in calculation of other fields The commerce product has the field: Price 

Then I added two more field: Quantity and Price per Unit

I need the field Price per Unit to take the calculated value from this: 

Price per Unit = Price/Quantity


How I get this?
Commerce out of the box has a quantity field and does by default a 'price-per-unit'. Watch this tutorial to give you an idea of how it works without any customizations. 

https://www.youtube.com/watch?v=3KEJcieG4jI