The average height of a semi-truck trailer is 13 feet 6 inches to 14 feet. There are no federal regulations on semi-truck heights, but there are roads that have lower clearances than the average height of a commercial motor vehicle.
The Department of Transportation for each state may impose height limits on semi-trucks and trailers. For example, the California Department of Transportation enforces a maximum height of 14 feet for all semi-trucks. On the other hand, the Pennsylvania Department of Transportation limits semi-trucks to be no taller than 13.5 feet.
The United Kingdom sets the maximum height for semi-trucks at 13.1 feet.