The two most common sizes for receiver hitches are 2" x 2" and 1.25" x 1.25". In order to determine the size of your trailer hitch, you can simply measure the height and width of its opening.
Class I and Class II trailer hitches typically have a 1.25" x 1.25" receiver opening. These hitches are most common on passenger cars, as well as smaller sport utility vehicles. There are a few types of Class II hitches with 2" x 2" receiver openings, although this is not common.
Class III and Class IV hitches are 2" x 2" and are the most common. Pick-ups, SUVs and some full-size sedans feature Class III and Class IV hitches.