The number of hamburgers that a McDonald's grill can cook at one time can vary based on the specific model and size of the grills used in their restaurants. McDonald's typically uses a variety of grills, including the clamshell-style grills that cook burgers from both sides simultaneously.
McDonald's used grills with different capacities, but a common configuration was the 24:1 grill, which can cook up to 24 burger patties at once. This means that when the grill is fully loaded, it can cook 24 hamburger patties in a single batch.
It's worth noting that McDonald's continuously updates their equipment and technology, so the specific grill models and capacities may have changed since then. For the most current information, I recommend checking directly with McDonald's or referring to their official website or press releases for any updates on their grilling equipment.