Unit of Measure Issue

Hi experts,

I have to calculate rate on unit quintal & my base unit of measure is EA But we purchase material from party in (candy)unit of product .Now I make po with with unit each & calculate price on quintal .We no rate of candy not quintal & relation is (1 candy x0.2812 )= rate of quintal.So where I fix this formula in standard sap system ? please help to solve issue

Thanks in advance