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Choosing between the two methods depends on the data you'd like to see. The average cost is the sum prices of all the products in inventory divided by the number of items. While the unit cost is the price when selling a particular product.
Additionally, I've included these articles that'll help you learn more about managing prices in QuickBooks:
Keep me posted if you need a hand with handling your inventory in QuickBooks. I'd be glad to help you some more.
