UPS says it will consider box size when setting prices for ground shipment of parcels within the U.S. and Canada.

The move announced Tuesday follows a similar change by rival FedEx.

United Parcel Service Co. believes that the change will push customers to put lightweight items in smaller boxes that take up less space on its familiar brown trucks, reducing the company's costs.

The change takes effect Dec. 29, after the big holiday-season shipping period. UPS already factors box size in rates for air shipments.

Packages have become lighter in relation to size over the past few years, which UPS says leads to higher costs and less efficient use of cargo space.

"UPS has been researching the potential expansion of dimensional-weight pricing for a number of years because it enables us to more appropriately align rates with costs, which are influenced by both the size and weight of packages," the company's chief commercial officer, Alan Gershenhorn, said in a statement.

Last month, FedEx Corp. announced that it would consider size and not just weight when pricing ground shipment of packages. Like UPS, FedEx was already considering size in rates for priority shipments.

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