Set and Display price per Kg

My products will have a few variant like 5kg pack, 10kg pack or 20kg pack and $/kg price for each will be different. My customers make a buying decision on basis of price of $/kg . I want to be able to set-up and display price $/kg for each product variant. How do i acheive this?

Example
Variant 1
5kg pack of sugar, price per kg = $ 1/kg, Total price = $5/pack

Variant 2
10kg pack of sugar, price per kg = $ 0.8/kg, Total price = $8/pack

You can using options to do that

Example
Option 1 : 1kg price is 1$

Or pm me with you store address may be can help you !