The chain is coming out with a bigger quarter-pounder patty that will weigh 4.25 ounces before cooking and have a new shape, making it more of a quarter-pounder plus, according to an internal document reviewed by CNBC.
The current patty stands at 4 ounces before cooking and shrinks to 2.8 ounces after cooking, according to McDonald's Twitter account. The chain also detailed new assembly procedures for the burger to make the searing more visible.
The new patties will roll out within the next month, according to one franchisee director of operations.
McDonald's declined to elaborate on the expanding burger.
"As (CEO) Steve Easterbrook has shared, we're always innovating around McDonald's food, drinks and restaurant experience based on customers' preferences, and that includes hotter food and reviewing cooking procedures, and we'll share more details soon," the company said in a statement.
So why is McDonald's tinkering with one of its most popular items?
The change "improves the taste, texture and appearance of the burgers" since the "patties retain more moisture resulting in a juicier and more flavorful burger," according to the document. The chain hopes the swaps will strengthen its core burger platform and increase burger sales.
McDonald's faces stiff competition in the burger segment as brands like Shake Shack, Sonic and Whataburger expand. Meanwhile, same-restaurant sales at McDonald's have continued to retreat, falling 2.4 percent year to date domestically.
The latest quarter-pounder moves provide more tangible evidence of just how McDonald's plans to turn around its struggling business. Easterbrook has already pledged to recommit to "tastier food across the menu." As part of this, he has said the chain will toast buns longer and change the way it sears and grills its beef.
It is also testing all-day breakfast, a top customer request, in some markets.
The quarter-pounder increase comes amid higher beef prices nationwide. During the first quarter, McDonald's noted U.S. commodity costs rose about 2 percent, due largely to higher beef prices, and the chain increased prices as a result.