The following formula is involved in the calculation of economic order quantities:

Economic order quantity (EOQ):
where D is the annual demand in units for the product or item, O is the fixed cost of placing and receiving an order, and C is the annual carrying cost per unit of the product or item.

The following references can be used to cite this economic order quantity (eoq) calculator:
 Soper, D.S. (2014) "Economic Order Quantity (EOQ) Calculator (Online Software)", http://www.danielsoper.com/fincalc. 
 DuBrin, A.J. (2008). "Essentials of Management", Mason, OH: SouthWestern Cengage. 