If the product has a UoS, I suggest using the quantity in that unit times the unit price to get the subtotal.
If you decide to use UoS, it means your sale unit price is against that UoS, not the UoM.
If the product has a UoS, I suggest using the quantity in that unit times the unit price to get the subtotal.
If you decide to use UoS, it means your sale unit price is against that UoS, not the UoM.