A standard semi truck in the United States is typically about 8.5 feet (102 inches) wide. This width applies to both the tractor and the trailer, allowing the vehicle to fit within a standard U.S. highway lane, which is usually 12 feet wide. While the maximum legal width is 8.5 feet in most states, trucks are allowed an additional 10 inches on each side for mirrors, making the total width including mirrors up to about 10 feet

. In summary:

• Standard width of semi truck (tractor and trailer): 8.5 feet (102 inches)
• Additional width allowed for mirrors: 10 inches on each side
• Total width including mirrors: up to about 10 feet

This width is consistent across most semi trucks to comply with federal and state regulations for highway travel