How to manage the difference of purchase item unit and sale item unit

In my bussiness, my purchase unit and selling unit are difference like purchase unit is bbl and selling unit is litre. But, I can only use one standard unit in inventory item. Even I create two different inventory items like (bbl) and crude (litre), I don’t know how to covert from one inventory unit to another. I am looking for some advice

you have two options

  1. create inventory with unit as litre and enter the purchase in litres itself even if its actually bbl.
    for example if 1 bbl is purchased you can manually enter the purchase as 158.987294928 litres.

  2. create two inventory items each for bbl and litre. use a production order to convert the required volume. for example, if you want to convert 1 bbl to litres, the finished good will be litre with quantity 158.987294928 and bill of material will be bbl with quantity 1.

read the guides section regarding production orders.

thank for your advice.