Well, the title is quite descriptive about what I'm trying to do with Rules for my e-shop. I have a flat rate for shippable products and I want to charge extra shipping costs to customers according to order's total weight. I'm already using physical fields for weight so I could use the field's value for this rule. Note that some products won't have anything in the weight field and in this case I don't want to take them into consideration for the shipping cost calculation.
So, I want to charge €3 (flat rate's base charge) if the order is 0-2 kilos. In case the total order's weight is more than 2 kilos, I want to add €1.2 to shipping cost for every additional kilo.
e.g. order has 3 products. Product 1 - 2 kilos Product 2 - 0 kilos (or no value in weight field) Product 3 - 2.5 kilos Total order's weight: 2+0+2.5 = 4.5 kilos (ie 2.5 kilos to be charged extra)
So the shipping charge should be €3 (flat rate's base) + €1.2*2.5 = €6.
I really need some guidance here on how I'm going to make this happen using Rules.