A system and method for dynamic quantity orders in an electronic trading environment are described. According to one method, a dynamic quantity order includes a price, a desired order quantity and a percentage associated with an estimated order quantity that will be filled in an order queue. When the order is received at an electronic exchange, the order is sorted into a pro-rata order queue, and the exchange may estimate a potential order quantity that will be filled in the order queue at the price based on the defined percentage. Subsequently, the exchange may then increase the order quantity of the dynamic quantity order so that if the estimated number of fills occurs, the order quantity of the dynamic quantity order will be filled.