Unit quantities

In my accounting/invoicing system, clients create product items.

Let's say you sell Apples You can sell single apples apples in a carton (e.g. 25 apples per carton) cartons of apples on a pallet (e.g. 50 cartons per pallets)

I would like to know how YOU handle the Quantity management. Do you create 3 different stock items or do you force people to enter 2 factors at invoice time. Qty and Factor, where factor can be (say) Single, Carton or Pallet.

When you *see* your product profile, do you see 1125 apples, X cartons and Y pallets and Z singles?

I hope I've explained this satisfactorily. If its NF, please forgive me.